OBSERVATIONS ON THE MINERALOGY AND GEOLOGY OF A PART OF THE UNITED STATES WEST OF THE MISSISSIPPI.

Extracted from a Report to Major Long[79]

The following remarks are designed to give a summary and connected view of the facts and observations collected during the progress of the exploring expedition, relative to the geology and mineralogy of the several regions traversed by the party, more particularly of the Rocky Mountains, and the western portions of the great valley of the Mississippi. In an attempt of this kind, some difficulty arises from the unsettled and progressive condition of geognostic science. A nomenclature, constructed upon principles applicable to the other branches of natural history, has been extended to this. Attempts have been made to define classes, orders, genera, and species of rocks; while it must be acknowledged, that the inventors of systems have hitherto failed to point out such infallible foundations for distinction of character as exist in the animal and vegetable kingdoms. Among minerals, from one extreme of the series to the other, there is a constant transition of approximating aggregates into each other. The particles of unorganized matter, being exempt from the influence of those peculiar laws which regulate the forms and characters of living {272} beings, and moving in obedience only to the impulses of attraction and affinity, arrange themselves together not always in an invariable order, and after a permanent and unalterable type, but are variously intermixed and confounded, as circumstances may have variously influenced their aggregation. Definitions, it must be acknowledged, have been constructed, strictly applicable to particular portions of matter, which may occur under similar circumstances in remote quarters of the globe. Fragments of granite may be found in the Rocky Mountains of America which could not be distinguished from the granite of Egypt, such as is seen in our collections. These definitions, then, may be sufficient for the purposes of the naturalist who confines his inquiries to his cabinet; but when examinations are extended, when we approach the imaginary limits of these artificial divisions, we not uncommonly find ourselves deserted by our boasted distinctions and definitions. It must be evident to any person in the slightest degree familiarized to the examination of the rocky materials composing the earth's surface, that between any two of the contiguous artificial divisions there is often-times no definite and discoverable boundary. Granite must consist essentially of felspar, quartz, and mica; so must gneiss and mica-slate; and between the two former, it is often extremely difficult to point out the line which shall be considered as marking the termination of the one and the commencement of the other. It will, we think, be acknowledged, that not one of the names applied to rocks, as constituting extensive strata, conveys of itself a definite and satisfactory idea. Hence the necessity which is felt, in attempting to give a detailed account of the rock formations of any particular district, to define the names in almost every instance of their application. If the following remarks should on this account seem faulty, by a certain monotony and appearance of {273} repetition, we hope there are a few, who, for the sake of the facts detailed, will excuse any want of precision in the language which may have necessarily resulted from the unsettled condition of the nomenclature.

No part of the earth, it is probable, presents a greater degree of simplicity and uniformity in the structure and conformation of its surface than North America. The mountain ranges are here distinct, forming each its own particular system, and preserving severally, through their whole extent, a similarity in external appearance, as well as in the structure and aggregation of the various rocks of which they are composed.

The outlines of a physical delineation of the continent of North America would present, first, the great chain of the Rocky Mountains, evidently a continuation of the Andes of the southern hemisphere, stretching parallel to the direction of the western coast from the isthmus of Panama to the northern ocean. Their summits penetrating far into the regions of perpetual winter, look down upon the vast plains of the Mississippi and its tributaries; in which we distinguish a comparatively inconsiderable range of rocky hills, commencing near the confluence of the Missouri and Mississippi, and running south-west of the Gulf of Mexico, near the estuary of the Rio del Norte. Beyond these, the surface subsides to a plain, stretching eastward to the commencement of the great chain of the Alleghanies. The range of the Alleghanies, far less elevated and alpine than that of the Rocky Mountains, traverses the continent in a direction nearly parallel to the Atlantic ocean, from the Gulf of St. Lawrence, on the north-east, to the confluence of the Alabama and Tombigbee rivers, in the south-west. Compared to the Rocky Mountains, this range is without summits, presenting, instead of conic peaks, long and level ridges, rising in no point to the inferior limit of perpetual frost, and scarce in any instance reaching that degree of {274} elevation which is incompatible with the growth of forests.

In many particulars there is a manifest resemblance between the Alleghanies, and the comparatively inconsiderable group known by the name of the Ozark mountains. They are parallel in direction, making an angle of about forty degrees with the great range of the Andes. They agree in having their most elevated portions made up of rocks of recent formation. It is well known, that, from the highly primitive gneiss rock at Philadelphia, there is a gradual ascent, across strata more and more recent, to the rocks of the coal formation, about the summit of the Alleghanies. Whether the same thing happens in every part of the range, our examinations have not yet been extensive enough to decide. We know that some of the granitic mountains of New England are far surpassed in elevation by the neighbouring hills and ridges of mica slate, talcose rocks, or even more recent aggregates.

In the Ozark mountains, as far as they have been hitherto explored, the granites and more ancient rocks are found at the lowest parts, being surmounted by those of a more recent date, the newest horizontal sandstone, and strata of compact limestone, forming the highest summits. What we wish to remark is, that the reverse of this being the case with the Rocky Mountains, the granite there far surpassing, both in extent and elevation, all the other aggregates forming the central and higher portions of all the ridges, that range has a character very distinct from the Ozark or Alleghany mountains.

It has been suggested by Major Long, that the hydrography of the upper portion of the Missouri seems to indicate the existence of a mountain range, approaching that river from the south-west, near the great northern bend, in the country of the Mandans. From Lewis and Clarke we have also some accounts tending to the confirmation of this opinion. Further {275} examination may perhaps prove this third range, called the Black hills, to resemble in direction and general character the Alleghany and Ozark mountains. The Rocky Mountains have not inaptly been called the backbone of the continent: these three lateral ranges, going off at an angle of about forty degrees, may with equal propriety be called the ribs. In latitude 38° north, the eastern base of the Rocky Mountains is found to be in about 106° west longitude: following the same parallel of latitude eastward, you arrive at the base of the Ozark mountains, nearly in longitude 94°. The intervening space, occupying the extent of near twelve degrees of longitude, is a wide and desolate plain, destitute of timber; scorched in summer by the reverberation of the rays of the sun, howled over in winter by the frozen west winds from the Rocky Mountains.

Though we have assumed twelve degrees of longitude as the medium width of this great plain, it is to be remarked, that to many parts of it our examinations have not been extended. In the latitude of 41°, no mountain, and scarce an elevation deserving the name of a hill, occurs between the western range of the Alleghanies and the Rocky Mountains. But at no great distance north of this parallel, low ranges of hills begin to appear in the region south-west of Lake Michigan; and though too inconsiderable in point of elevation to deserve particular notice, still they exhibit peculiar characters, which seem to designate an intimate connection with the Ozark mountains, south of the Missouri. The same succession of strata, the same alternation of crystalline beds, with those of mechanical deposition, and similar depositories of metallic ores, are observed here, as in the regions about the Merameg and St. Francis. A marked difference is also, as we think, to be discovered between the rocks and soils on the different sides of this range. Of this we shall speak more {276} particularly in another place. For our present purpose, it is sufficient to assume as a boundary of the region we propose first to consider, a line running from the confluence of the Arkansa and Canadian rivers on the south-west, to the junction of the Mississippi and Wisconsan, on the north-east. Assuming this as the direction of the range of the Ozark mountains, it will be perceived, by examining the map, that to the north-west of this line spreads an extensive plain, reaching to the base of the Rocky Mountains. This plain has been crossed in three different places by the exploring party, as already detailed in our narrative; once in ascending by the River Platte, between latitude 40° and 41° 30´; again, in descending the Arkansa, in 38°; and, thirdly, by the route of the Canadian, in 34°. To the information collected in these journeys, we have added a little from other sources; but the greater part of this extensive region yet remains unknown.

Of the Great Desert at the base of the Rocky Mountains

The portion of country which we design to consider under this division has an average width of five or six hundred miles, extending along the base of the Rocky Mountains from north to south: as far as we have any acquaintance with that range, consisting entirely of granitic sands, or of secondary aggregates made up of the detritus of that great chain of primitive mountains, there seems to be a degree of propriety in designating it by some name recognising relation to those mountains. It has been mentioned as the "Mexican desert;" a name sufficiently applicable, perhaps, to some portions of it, but one by no means to be extended to every part alike, as there can be little doubt of its occupying an extensive {277} portion of the interior of North America. That a similar desert region exists on the western side of the mountains, we have sufficient evidence; but whether as uninterrupted and as extensive, we have not the means of determining.

The Jesuit Venegas, speaking of the early history of California, says "Father Kino and his companions, after travelling thirty leagues from San. Marcelo, came to a small rancheria (Indian village); and leaving on the north the great mountain of Santa Clara, whose sides, for the length of a league, are covered with pumice-stone, they arrived at the Sandy Waste, on the 19th of March." Our information is, however, too limited to justify an attempt to fix the boundaries of this desert; we will, therefore, content ourselves with communicating the observations our opportunities have enabled us to make.

The channel of the Missouri, near the mouth of the Platte, discloses here and there rocks of horizontal limestone; which, from their peculiar character, we are disposed to consider as belonging rather to the Ozarks, than having any connection with the Rocky Mountains. These rocks appear at the lowest parts of the valleys, and are usually surmounted by extensive beds of soil, consisting principally of flinty sand in the most minute state of division, but variously intermixed with the remains of organized beings, and sometimes with calcareous and aluminous earth. Proceeding westward, the sand becomes deeper and more unmixed; not a rock or a stone, in place or out of place, is to be met with for some hundreds of miles. It is believed that no rocky bluffs appear along the valley of the Platte, within three hundred miles of its mouth, though a small part of this distance, on the lower portion of the river, has not hitherto been explored. The surface is not an absolute plain, but is varied with gentle undulations, such {278} as the draining of water, from an immense table of a light arenaceous earth, for a succession of centuries, may be supposed to have occasioned. The gradual intermixture of the exuviÆ of animals and vegetables, with what was formerly a pure siliceous sand, has at length produced a soil capable of supporting a scanty growth of grasses; now almost the only covering of these desolate regions. Scales of mica, little particles of brownish felspar, and minute fragments of hornblende, may here be detected in the soil.

About four hundred miles west of the mouth of the Platte, a low range of sandstone hills crosses the country from south-west to north-east. The strata composing these hills have no perceptible inclination, and present appearances which indicate their deposition to have been nearly contemporaneous to that of many of our coal formations. It has already been suggested that this range may probably be a continuation of the Cotes Noir, or Black hills, said to contain the sources of the Shienne, the Little Missouri, and some branches of the Yellow Stone.[80]

These inconsiderable hills being passed, the surface again subsides nearly to a plain. The fine and comparatively fertile sand which prevailed to the east of the ranges, is exchanged for a gravel made up of rounded granitic fragments, varying in dimensions from the size of a six-pound shot to finish sand. This great mass of granitic fragments, evidently brought down by the agency of water from the sides and summits of the Andes, slopes gradually from their base, appearing, as far as examinations have extended, to correspond in some measure, in magnitude, to the elevation and extent of that part of the mountains opposite which it is placed. The minute particles derived from the quartzy portions of the primitive aggregates, being least liable to decomposition, have been carried to the greatest distance, {279} and now form the almost unmixed soil of the eastern margin of the great sandy desert. The central portions are of a coarser sand, with which some particles of felspar and mica are intermixed: nearer the mountains, pebbles and boulders become frequent, and at length almost cover the surface of the country.

The opinion above advanced, that the great sandy desert has resulted from the wearing down of the mountains, both before and since the retiring of the ocean, should, perhaps, be received with some caution. We have no foundation for the belief, but in the examinations which enabled us to discover that the materials composing both regions are similar in kind; that the granitic soils of the plain are precisely such as would result from the disintegration of the rocks now existing in the mountains; and that the numerous deep ravines and water-worn valleys traversing the mountains in various directions, indicate the change here supposed to have happened.

It is probable many parts of this extensive desert may differ from that traversed by the Platte, in having the surface more or less covered with horizontal strata of sandstone and conglomerate, instead of loose sand and pebbles. Indeed, there are many appearances indicating that a formation of this kind formerly extended down the Platte much farther than at present. From the minute account given in the narrative of the expedition, of the particular features of this region, it will be perceived that its eastern portions bear a manifest resemblance to the deserts of Siberia. The soils, and I believe the rocks, wherever any occur, are saline: plants allied to chenopodium and salsola are peculiarly abundant, as are the astragali and other herbaceous leguminÆ; while trees and forests are almost unknown.

The surface of the sandy plain rises perceptibly towards the base of the mountains; and becoming constantly more and more undulating, is at length broken, disclosing some cliffs and ledges of micaceous {280} sandstone. Near the Platte this sandstone occurs in horizontal strata, sometimes divided by the beds of the streams, and forming low ridges parallel to the Rocky Mountains. Whether they continue in an uninterrupted line along the base of the mountains, we have not been able to ascertain. They are separated from the first range of primitive, by more elevated cliffs of a similar sandstone, having its strata in a highly inclined position. Behind these, occur lofty but uninterrupted ranges of naked rocks, destitute of any covering of earthy or vegetable matter, and standing nearly perpendicular. At a distant view, they present to the eye the forms of walls, towers, pyramids, and columns, seeming rather the effects of the most laborious efforts of art, than the productions of nature. When surveyed from the more elevated summits of the first granitic range, these immense strata of sandstone standing on edge, and sometimes inclining at various angles towards the primitive, resemble the plates of ice often seen thrown into a vertical position in the eddies and along the banks of rivers.

Climbing to the summits of such of these elevations as are accessible, and crossing their stratifications towards the primitive, we observe appearances similar to those found in the valleys, when circumstances enable us to push our inquiries to a corresponding extent below the surface. Having crossed the upturned margin of the whole secondary formation which occupies the plain, and arriving at the primitive, we find these highly inclined strata of sandstone reposing immediately against the granite. We search in vain for any traces of those rocks distinguished by the Wernerians as rocks of the transition period. We also observe an entire deficiency of all those primitive strata which the doctrine of universal formations may have taught us to look for in approaching the granite.

The sandstone along the base of the mountains, {281} though apparently not very recent, contains the remains of marine animals and plants, and embraces some extensive beds of puddingstone. It may be remarked that the sand and gravel composing these aggregates have in general the same close resemblance to the materials of the granitic mountains, as we have already observed in the un-cemented materials of the plain. Indeed, it does not seem easy to determine whether the sands, gravel-stones, and pebbles, now loosely strewed over the extensive plains of the desert, have been brought down immediately from the granitic mountains whence they were originally derived, or have resulted from the disintegration of the stratified sandstone and conglomerates deposited during a long series of ages, while the waters of the ocean rested upon the great plain, and washed the bases of the Rocky Mountains. The very wide and equal distribution of these sands, in other words, the very gradual slope of the dÉbris of the mountain, would seem to countenance the latter supposition.

The position of the strata of sandstone varies in the distance of a few miles from nearly horizontal to an inclination of more than sixty degrees, and that without any very manifest change of character, or the interposition of any other stratum. The laminÆ most distant from the primitive, occupying the eastern sides of the first elevations, though lowest in actual elevation, may with propriety be considered the uppermost, as resting on those beyond. At the level of the surface of the great plain, they sink beneath the alluvial; and in the neighbourhood of the river Platte, they are no more seen. The uppermost are of a yellowish-gray colour; moderately fine; compact and hard; constantly varying, however, at different points, in colour as well as most other characters. The light-coloured varieties usually contain small round masses about the size of a musket-ball, which are more friable than the rock itself, {282} from which they are easily detached, leaving cavities corresponding to their own shape and dimensions. They are commonly of a dark-brown colour, and of a coarser sand than that which constitutes the rock itself. Where these are found, I could never discover any of those remains of shellfish so distinctly seen in many of the secondary rocks in this neighbourhood.

Passing downwards, or in other words, proceeding towards the primitive, crossing the edge of the secondary, the sandstone becomes more coarse and friable, its colour inclining more to several shades of brown and red. This variety contains numerous masses of iron ore, and does not appear to abound in the remains or impressions of organized beings. It is also less distinctly stratified than that just mentioned; and it often becomes exceedingly coarse, with angular fragments intermixed, being in no respect different from the rock denominated breccia, and by some geologists considered a distinct stratum.

This tract of sandstone, which skirts the eastern boundary of the Rocky Mountains, and appears to belong to that immense secondary formation which occupies the valley of the Mississippi, abounds in scenery of a grand and interesting character. The angle of inclination of the strata often approaches 90°, and is very rarely less than 45°. That side of the ridges next the primitive appears to have been broken off from a part of the stratum beyond; and is usually an abrupt and perpendicular precipice, sometimes even overhanging and sheltering a considerable extent of surface. The face of the stratum is usually smooth and hard, and both sides are alike destitute of soil and verdure. Elevations of this description are met with, varying from twenty to several thousand feet in thickness; neither are they by any means uniform in height. Some of them rise, probably, three hundred or four hundred feet; and considering their singular character, would appear {283} high, were they not subjected to an immediate and disadvantageous comparison with the stupendous Andes, at whose feet they are placed. Their summits in some instances are regular and horizontal, and are crowned with a scanty growth of cedar and pine. Where the cement and most of the materials of the sandstone are siliceous, the rock evinces a tendency to break into fragments of a rhombic form; and in this case the elevated edge presents an irregularly notched or serrated surface.

Sandstones consisting of silex, with the least intermixture of foreign ingredients, are the most durable. But in the region of which we speak, the variations in the composition, cement, and characters of the sandstone, are innumerable. Clay and oxide of iron entering into its composition in certain proportions, seem to render it unfit to withstand the attacks of the various agents, whose effect is to hasten dissolution and decay. Highly elevated rocks of this description may well be supposed in a state of rapid and perceptible change. The sharp angles and asperities of surface which they may have originally presented, are soon worn away; the matter constantly removed by the agency of water from their sides and summits is deposited at their feet; their elevation gradually diminishes, and even the inclination of their strata becomes at length obscure or wholly undiscoverable. This appears to have been a part of the process by which numerous conic hills and mounds have been interspersed among the highly inclined naked rocks above mentioned. These hills, often clothed with considerable verdure to their summits, add greatly to the beauty of the surrounding scenery. The contrast of colours in this rude but majestic region, is often seen to produce the most brilliant and grateful effects. The deep green of the small and almost procumbent cedars and junipers, with the less intense colours of various species of deciduous foliage, acquires new beauty from being {284} placed as a margin to the glowing red and yellow seen in the surfaces of many of the rocks.

Of the Sandstones of the Rocky Mountains

Having commenced our account of the Rocky Mountains with the consideration of that vast accumulation of rounded fragments constituting the Great Desert, which may be reckoned the most recent formation connected with that great range of mountains, we proceed to speak of the sandstones, the next member in the inverted order we have adopted; and here we take occasion to remark the peculiar grandeur and simplicity of features which distinguish the mineral geography of this part of our continent. We have here a stupendous chain of granitic mountains, many hundred miles in extent, and with no stratified rocks resting about their sides, except a few sandstones, equally granitic, and almost equally primitive. We discover here comparatively few traces of that magnificent profusion of animal and vegetable life, which in other parts of the globe has reared mountains of limestone, clay-slate, and those other aggregates, which if not entirely, are often in a great measure, made up of the exuviÆ of living beings. We shall not here be understood to contradict the assertion we have before made, that the sandstones along the base of the Rocky Mountains contain organized remains, and bear abundant evidence of having been at a comparatively recent period deposited gradually from the waters of the ocean. The particular we wish to remark as distinguishing these mountains most strikingly from the Alleghanies, and many other ranges, is the entire want of the aggregates referred by the Wernerians to the transition period, as well as nearly all the stratified primitive rocks, and the limestones of the secondary formations.[81] This great range, as far as hitherto known to us, lies nearly from north to south. Considered {285} topographically, the sandstone formation belongs both to the mountains and the plains, sloping down from the sides of the granite, and disappearing under the sands of the Great Desert.

The western boundary of this formation of sandstone, as far as our examinations have searched, appears to be defined, and corresponds to the side of the easternmost granitic ranges. From the Platte towards the south, the sandstone increases in width, and on the Canadian it extends more than half the distance from the sources of that river to its confluence with the Arkansa. This sandstone formation we consider as consisting essentially of two members.

1st. Red sandstone.—This rock, which is the lowest of the horizontal or fletz rocks met with in this part of the country, is very abundant in all the region immediately subjacent to the Rocky Mountains. We have never met with a similar rock in the eastern part of the valley of the Mississippi. It occurs at intervals along the base of the mountain, reposing against the primitive rocks, in an erect or highly inclined position. It varies in colour from bright brick red, to dark brown; and is sometimes found exhibiting various shades of yellow and gray. It is, however, almost invariably ferruginous; and the predominance of red in the colouring certainly entitles it to the distinctive appellation of red sandstone. The lowest part of the stratum has frequently least colour, and is also the most compact and hard. This is not, however, invariably the case; for in the neighbourhood of the Platte, that part of it which lies immediately upon the granite is white, and contains beds of coarse conglomerate or puddingstone. At the lowest points we have been able to examine, are found embodied large oval or irregular masses of hornstone, usually of a yellowish-white, or bluish colour; and near the surface of these masses are found the few well-marked organic relics the stratum can be said to contain. Higher {286} up the rock becomes much softer, and usually of a browner colour. It is disposed in immense horizontal laminÆ or strata, which, when broken transversely, exhibit some tendency to separate into fragments of a rhombic form. Near the upper part of the stratum are frequently seen broad belts of a lighter colour, conspicuously marked with reticulating yellowish veins. The cross fracture of the stone is even and earthy, except in the conservatories. When divided in a direction parallel to that of the strata, small scales of mica are seen; but this is usual only in those parts of the stone where natural seams or fissures existed. Small specimens from many parts of this stratum could not be distinguished from the red sandstone quarried at Nyae in New Jersey, and used in great quantities in the cities of New York, Albany, &c. for building. The character which most particularly distinguishes this rock from "the old red sandstone of Werner," pointed out by Maclure in New York and New Jersey, appears to be the constant accompaniment of gypsum, and muriate of soda; the colour of the stratum is also in general of a brighter red, approaching vermilion, and is more copiously imparted to such streams of water as traverse it.

2d. Argillaceous or gray sandstone.—Immediately above the red sandstone, we have invariably found, where any rock rests upon it, a grayish or yellowish-white sandstone, which we distinguish as the second variety. It most frequently contains a large proportion of argillaceous earth in the cement, and has a more or less slaty structure. Hence it may with propriety be denominated argillaceous sandstone, though it may in some respects differ from the rock known to many by that name. This variety being uppermost in actual position, is perhaps more frequently seen than the other, while at the same time it is probably less abundant. The line of separation betwixt the two is often manifest and well defined; and in other instances, they pass by imperceptible gradations into each other. {287} The upper, or gray sandstone, is usually more compact and homogenous than the red; it breaks like the other, though more rarely, into large cubic or rhombic masses, which, on account of the more compact texture of the stone, retain their form longer than those of the other variety. The precipices formed by both are often lofty and perpendicular; but the projections and angles of the red are more worn and rounded than those of the gray. The narrow defiles and ravines which the streams of water have excavated, are less tortuous when they are made entirely in the gray sandstone, than in other instances. The springs of water flowing from it are more free of mineral impregnations, than such as are found in the other variety. It sometimes consists of glittering crystalline particles, but does not in this case appear to be a chymical deposit. In fine, it appears under an endless variety of characters, of which it would be in vain to attempt the enumeration. Although the gray sandstone is not invariably distinguished by the presence of an argillaceous ingredient, yet it is constantly found accompanying soft clay-slate, or bituminous shale and coal, wherever these last are met with.

If this formation of sandstone, consisting of the two varieties just mentioned, ever extended across the valley of the Mississippi to the Alleghany mountains, as some might be disposed to believe, we cannot pretend to determine what was its position relative to the immense masses of fletz, limestone, and other rocks now found in that valley. But as the red variety is still extensively disseminated, and usually accompanied by those valuable substances, salt and plaister, it may not be amiss to trace, as far as our examinations have enabled us to do it, the outline of the region which it occupies. As we have before mentioned, it is found in the vicinity of the river Platte, in a highly inclined position, covering a narrow margin immediately at the foot of the Rocky Mountains. {288} From the accounts of Lewis and Clarke, we are induced to believe that it exists under similar circumstances, near the falls of the Missouri. On the Canadian it is constantly met with, from the sources of that river on the borders of New Mexico, near Santa FÉ, 106° west, until you arrive within a short distance of its confluence with the Arkansa, in long. 97° west. The waters of the Canadian, from flowing over the sandstone in question, acquire an intense red colour, and are so impregnated with muriate of soda and other soluble salts as to be unfit for use. This, we are credibly informed, is also the case with the waters of three small rivers tributary to the Arkansa, above the Canadian, on the same side; also with the waters of Red river. Hence the conclusion appears to be justified, that this rock extends from near the Arkansa on the north, to a point beyond Red river on the south; and from near the mouth of the Canadian, an unknown distance to the west. It is not unlikely it may exist about the sources and upper branches of the Rio Colorado of California, the Red river of Santa FÉ, and the other Red rivers of New Mexico. Near the mountains, and for a great distance to the south and east of the High Peak, it is covered by the gray sandstone already mentioned. This gray sandstone is the uppermost of those horizontally stratified rocks which are seen in this region, possessing convincing evidence of their being the deposition of an ocean or lake of salt water.

Perhaps the most striking feature of this formation of sandstone, is the great and abrupt change in the inclination of the strata in the parts near the granite. We have already described this in a manner sufficiently explicit, as we suppose, to convince most of our readers that since the deposition of the sandstones, a signal change must have happened in the elevation of the secondary aggregates as compared with the granite. The appearances are precisely {289} such as we must suppose would have ensued, had the sudden emerging of the granite broken off, and thrown into an inclined or vertical position the margin of the horizontally stratified rocks of the plains. We are conscious that inclined strata of sandstone are by no means infrequent about the declivities of lofty mountains, but we are not well assured that the same strata being traced to a little distance, are often found in a horizontal position in the plains, as is the case in the instance under consideration.

It may perhaps be thought possible that the gradual wearing away, by the agency of rivers, of some portions of the sandstone, may have been sufficiently extensive to have occasioned that change of elevation of which we speak; and that those rocks now found in an inclined position, are insulated portions of what was formerly the upper part of the stratum, which having been undermined on their eastern side, and supported by the granite on their western, have fallen into their present situation.

This supposition, however, seems incompatible with the vast magnitude and extent of these rocks, and entirely irreconcilable to the fact that they dip to a great and indefinite extent below the present level of any of the beds of the river.

The position of this formation in relation to the granite is similar to that of the sandstone of Guachaco, in South America, observed by Humboldt; also to that spoken of by Mr. Burkhardt, at the entrance of Nubia, superimposed upon the granite of Syene, and to that mentioned by Mr. Schoolcraft, as found near Lake Superior, but it does not appear that those formations have the same peculiarities in regard to inclination.

FLETZ TRAP ROCKS

Another family of rocks, of recent formation, and connected with the sandstone last mentioned, remains to be noticed.

{290} These are rocks of basaltic conformation, belonging to the class, by some mineralogists denominated superincumbent rocks, and by many considered of volcanic origin. They present a striking contrast, by their dark colour, by the vastness and irregularity of their masses, to the smooth, light, and fissile sandstone on which they rest. Sometimes they are observed compact and apparently homogeneous in their composition, and in many particulars of structure, form, hardness, &c. seeming more analogous to the primitive rocks than to those recent secondary aggregates with which they are associated. In other instances, black and formless masses of porous and amygdaloidal substances are seen scattered about the plains or heaped in conic masses, but having no immediate connection with the strata on which they rest. Most of the rocks belonging to this class were observed in the neighbourhood of the sources of the Canadian. Among them we distinguish two kinds, referable to the two divisions called greenstone and amygdaloid.

1. Greenstone, Jameson.—It appears in the limited district we examined under almost every variety of form and character noticed by mineralogists. Sometimes it is nearly or quite free from any intermixture of hornblende, is of a fine dark green colour, and closely resembles some varieties of serpentine. Sometimes its colour is a dull gray, graduating into brown and black of various shades and intensities. It forms numerous conic hills of considerable elevation, scattered without order, or grouped in various directions. These hills are usually of a regular and beautiful form. The great plain on which they are based is elevated and destitute of timber or water, but ornamented with a carpet of thick and verdant grasses. The hills, though steep and high, are sometimes smooth and green to the summit, the surface on all sides being unbroken by trees or rocks, and covered with thick turf. The whole forms a scene of singular {291} beauty. During our journey across the district, based upon the rocks now under consideration, we had constantly occasion to admire the freshness and abundance of the grasses and other herbaceous plants. The plains of the Platte and Arkansa we had seen brown and desolate, as if recently ravaged by fire; but here we passed elevated tracts, where, for many miles, we could find no water for our own necessities, yet the vegetation possessed the freshness of spring in the most fertile regions. But the conic hills just mentioned, are not invariably the form under which the greenstone appears. It sometimes rises in low irregular ridges, extending a considerable distance, and sloping on both sides into the level of the plain.

In the narrow channels which the streams of water have sunk in it, may be seen perpendicular precipices of great elevation, but the valley between them is usually almost filled with large broken masses of the rock, which frequently exhibit a prismatic form. It falls readily into large masses, but seems strongly to resist that progress of disintegration which it must undergo before it can be removed by the water. The face of the perpendicular precipices are almost invariably marked by distinct and large seams running nearly parallel to each other, and at right angles with the horizon. Following the watercourses, which are sunk considerable distance below the surface, the line of separation from the sandstone on which the greenstone rests, at length becomes visible on account of the descent of the surface.

2. Amygdaloid, Kirwan, Jameson.—We apply this name to a porous or vesicular rock, of a very dark gray, greenish or black colour, usually found near the greenstone, but sometimes in connection with the sandstone. In its ultimate composition it resembles greenstone, but we have never seen in it such large fragments of felspar and scales of mica, as are observed in that rock. The amygdaloidal {292} cavities which every where penetrate this rock, are of various sizes, some of them appearing like bubbles which have been formed in a semifluid mass, and afterwards lengthened and variously distorted by the motions of the contiguous matter. Near the surface they contain a soft white, or yellowish white substance, very different from the rock itself, usually a soft chalk-like carbonate of lime. This gives the recent surface a mottled appearance. In surfaces which have been for some time exposed to the air, this soft substance has been removed, and the pores and vesicles are found empty.

Amygdaloid does not appear to occupy any very great extent of the country near the Rocky Mountains. We have not met with it imbedded in, or surmounted by any other rock. Like the greenstone, it forms conic hills which sometimes occur in deep water-worn vallies, bounded on both sides by perpendicular walls of sandstone. It is likewise seen in the high plains, sometimes in the form of narrow and crooked ridges, apparently following what were anciently the beds of small brooks. Some very high and sharp conic hills were visible to the westward, but at a great distance. Two of this kind which stand near each other, and seem to be detached from the primitive mountains, are called the Spanish peaks, and at the end of July, snow was still to be seen on them.

When either of the two rocks last mentioned occur, it is not uncommon to find detached masses of a stone somewhat resembling the pumice-stone of commerce. It is usually of a faint red, or yellowish white colour, but sometimes it is brown, or nearly black. It feels less harsh than the pumice-stone which is used in the arts, and seems to consist in a great degree of clay. It appears to be entirely similar to the substance brought down the Missouri by the annual floods, and by many considered as a {293} product of pseudo-volcanic fires, said to exist on that river.

With regard to the soils resting upon the rocks of this trap formation, it may be worthy of remark, that gravel and water-worn pebbles rarely occur, except in situations where it is easy to see they may have been derived from the substratum of sandstone. We are not disposed to enter into any discussion concerning the origin of the trap rocks. The volcanists, and those who believe the trap formations to have been thrown up in a state of fusion from beneath the crust of the earth, will have an easy method of accounting for a fact mentioned in our journal, namely, that pieces of charred wood were found enclosed in the sandstone underlying the formation in question. Though we sought in vain for some evidence that the rocks of this formation traversed the strata of sandstone in the manner of the whin dikes of England, we are conscious our examinations were far too limited to justify us in asserting that this is not the case; nor can we adduce a single fact from which it could be inferred that these basaltiform rocks have been deposited, like the accompanying strata of sandstone, from suspension in water. The country occupied by this formation, exhibits scenery of a very peculiar and interesting character. It is remarked by Humboldt,[82] that "in the Canary islands, in the mountains of Auvergne, in the Mittelgebirge, in Bohemia, in Mexico, and on the banks of the Ganges," and we may add, in the United States, the formation of trap is indicated by a symmetrical disposition of the mountains by truncated cones, sometimes insulated, sometimes grouped, and by elevated plains, both extremities of which are crowned by a conical rising. In some of the unpublished drawings by Mr. Seymour, these peculiar {294} features of the scenery of the fletz trap formation, have been preserved.

RECAPITULATION

The secondary formations along the eastern base of the Rocky Mountains, are:

1st. Red Sandstone—Rests immediately upon the granite, is rather indistinctly stratified; strata sometimes inclined and sometimes horizontal; abounds in gypsum, salt, and iron, but exhibits no indications of coal.

2d. Argillaceous, or Gray Sandstone—Overlays the red, conforming to it in the inclination of the strata, occurs principally near the primitive; contains coal and iron.

3d. Greenstone and Graystone[83]—Of an imperfectly columnar structure, resting on the argillaceous sandstone.

4th. Amygdaloid—Sometimes containing argil, and sometimes hornblende, occurs with the greenstone about the sources of the Canadian river, constituting with the former the newest fletz trap formation.

5th. Sand and Gravel—Accompanying the sandstones and extending over the great desert, but rarely found resting on the trap rocks.

The sandstones being entirely mechanical aggregates, consisting of rounded fragments of rocks formerly constituting a part of the primitive mountains, would seem to have been deposited at a very remote period, when the waters of the primeval ocean covered the level of the great plain and the lower regions of the granitic mountains.

Subsequent to the deposition of the horizontally stratified rocks, the position of these in relation to the primitive, has been somewhat changed either by the action of some force beneath the primitive rocks, {295} forcing them up to a greater elevation than they formerly possessed, or by the sinking down of the secondary, produced by the operation of some cause equally unknown. Without supposing some change of this kind, how can we account for the great inclination of the margin of the sandstone rocks which is found resting against the granite almost perpendicularly? Nearly contemporaneous to this change, was the retiring of the sea, and the formation of the trap rocks. The beds of loose sand and gravel which are still constantly accumulating, have been formed in part from the disintegration of the sandstones and puddings, and partly by the action of those currents of water which are constantly bringing down small fragments from the primitive rocks, and depositing them in the plains.

The absence of any formation of limestone is a distinguishing characteristic of the country under consideration. A traveller to the upper part of the Missouri mentions "calcareous and petrosiliceous hills," as existing in the coal districts on that river. But in ascending the Platte from its confluence with the Missouri to the mountains, we saw not a single fragment of limestone. Small veins of carbonate of lime crystallized in the usual form, are met with in the argillaceous sandstone of the Arkansa, also the sulphate in small quantities. Gypsum is very abundant on the Canadian river, at a distance of three or four hundred miles from the mountains. It is disseminated in veins and thick horizontal beds in the red sandstone. The extent and thickness of these horizontal beds are, perhaps, such as would justify the appellation of stratum, but as it is not met with in great quantities, except in connection with the sandstone, with which it often alternates, it may with propriety be considered a subordinate rock.

Rock Salt.—This substance has often been said to exist in some part of upper Louisiana, in the form of {296} an extensive stratum: we have met with salt among the natives in masses of twenty or thirty pounds weight. The interior of these masses when broken, presented a crystalline structure, being made up of incomplete cubic crystals variously grouped together. On one of the surfaces, which had probably been the one in contact with the ground or rock on which the salt had rested, a considerable mixture of red sand was discoverable. These masses had apparently been produced by the evaporation, during the dry season, of the waters of some small lake. The whole country near the mountains abounds in licks, brine springs, and saline efflorescences, but it is in the neighbourhood of the red sand-rock before mentioned, that salt is met with in the greatest abundance and purity. The immediate valley of the Canadian river in the upper part of its course, varies in width from a few rods to three or four miles, but it is almost invariably bounded by precipices of red sand-rock, forming "the river bluffs." In the valley between these, incrustations of nearly pure salt are often found, covering the surface to a great extent, in the manner of thin ice, and causing it to appear when seen from a distance, as if covered with snow.

Most of the remarkable formations of rock-salt hitherto known, have been found in the stratum denominated "the lowest red sand rock," which appears to correspond in character, position, &c. with the sandstone above mentioned. Rock salt is found in connection with this sandstone in Cheshire, and at Northwich and Droitwich, in England, at Cardona in the province of Catalonia in Spain, and at the base of the Carpathian mountains in Moldavia and Poland. In Peru it is accompanied by sandstone and gypsum.

Accident, or further examination, it is probable, may hereafter bring to light those extensive beds of {297} this substance, which there is reason to believe exist in the neighbourhood of the Rocky Mountains. The briny character of those great streams, the Arkansa and Red rivers, flowing over the red sandstone formation, and receiving from it the peculiar character and colour of their waters, affords sufficient evidence of the existence of such beds, and the greatness of the quantity washed away in any given time, would lead to the conclusion, that they must be of vast extent. By the analogy of other rock salt formations apparently similar in character, we should be instructed to search for these beds in depressed situations and basin-shaped cavities, whose contents had not been worn down and removed by the currents of water.

Other secondary rocks found in different parts of the great valley of the Mississippi will be noticed hereafter. Those above enumerated seem to have a peculiar dependence upon the Rocky Mountains, and for this reason, we thought proper to consider them in connection with that range; they also appear to be, in some measure, independent of the other members of that great secondary formation on the borders of which they occur. The peculiar features of the region occupied by these rocks have been minutely described in the narrative of our journey. It is a region unfitted by the barrenness of its soil, the inhospitable character of its climate and other physical disadvantages, to become the residence of a permanent and numerous population. The immense grassy plains of the southern and eastern portions are adapted to the feeding of cattle and horses; and it is not improbable the countless herds of bisons and wild horses will soon give place to domesticated animals. The coal, salt, plaster, and iron, which constitute the mineral wealth of this portion of the United States' territory, lose much of their value on account of their remoteness from navigable streams. Beautiful carnelions and agates occur in the alluvial regions of {298} the Platte and the Missouri; but these will never become objects of any importance.

Of the Ozark Mountains

Leaving the newest fletz trap rocks, about the sources of the Canadian, and returning eastward along the great woodless plain between the Arkansa and Red rivers, we find an extensive tract occupied exclusively by the red sandstone of the salt formation. This rock, as we have already remarked, is constantly accompanied by gypsum and muriate of soda. The red and somewhat argillaceous soil which results from its disintegration is far more fertile than that of the gravelly plains of the Platte, being often covered with a luxuriant growth of grasses, and affording pasturage to great numbers of herbivorous animals.

About one hundred and fifty miles west from the confluence of the Arkansa and Canadian, this red sandstone is discontinued, being succeeded, or perhaps overlaid by an extensive coal formation. The argillaceous sandstone of this formation assumes various characters at different points. The Falls of the Canadian, particularly described in our narrative, are occasioned by a small ridge of fine argillaceous sandstone of a deep green colour, crossing the bed of the river obliquely. The coal beds in this region are of great thickness, and are apparently extensive and numerous. This formation appears, in a great measure, unconnected with the coal strata along the base of the Rocky Mountains, and the sandstone of the two districts are often remarkably dissimilar. Though the strata in both instances are nearly horizontal, the formation at the base of the Rocky Mountains must have an actual elevation greatly surpassing that of the district now under consideration. For these reasons, we have been induced to consider {299} this as belonging to the small group of mountains we have already had frequent occasion to mention, and which have received from Major Long, the name of Ozark mountains. These we shall now proceed to describe, according to the information in our possession.

From an inspection of the map annexed to this work, it will be perceived that the course of the Missouri, below the mouth of the Konzas, is considerably inflected to the east, in order to pass round the end of a range of hills, rising in the angle between this river and the Mississippi. This range increases in elevation for some distance to the south-west, its highest point being somewhere near the sources of the White and Osage rivers, the two most considerable streams originating in these mountains. Farther to the south-west, losing a part of its elevation, it is traversed in succession by the Arkansa and Red rivers from the west, and gives origin to the Washita, the Sabine, and some other rivers of inconsiderable magnitude. Our acquaintance with the country between Red river and the Rio del Norte is too imperfect to enable us to trace particularly the continuation of the Ozark mountains, which is believed to extend to that river, and to have some connection with its great southern bend, below the confluence of the Rio Conchos. We will, therefore, at present, confine our attention to that portion north-east of Red river. Though there is no point of great elevation in any part of the range, the whole is truly a mountainous region, and well entitled to a distinctive appellation. Its parallelism in general direction to the Atlantic coast, and the great chain of the Alleghanies, as well as the character and inclination of its component strata, afford unequivocal indication that it belongs to a different system from the great chain of the Rocky Mountains. In several particulars, there is a striking resemblance between this range and the Alleghanies, {300} and in some, as we shall notice hereafter, as manifest a dissimilarity.

Near the western limits of the coal formation, which are also the limits of the mountainous countries on the Canadian and Arkansa, compact limestone occurs for the first time (as far as our acquaintance extends) on this side the Rocky Mountains. This formation of limestone, and the accompanying strata of argillaceous sandstone, though they do not, perhaps, always strictly coincide in position, may be traced far to the north; and these we consider as marking the western limits of the Ozark mountains. It is to be remarked, however, that in these observations, we do not intend to apply this name with strict geographical precision to those portions only which are sufficiently elevated to be called mountains; but so far to extend its signification as to include not only the high and broken ridges, but several less elevated tracts possessing the same peculiar mineralogical features.

The few facts and observations we have it in our power to contribute towards an account of this interesting range, were collected during a pedestrian excursion from Bainbridge on the Mississippi, through the country of the lead-mines, at the sources of the Merameg and St. Francis, and a journey from Belle Point, by the way of the hot springs of the Washita, and the upper settlements of White river, to Cape Girardeau. For many important facts we are indebted to Major Long's unpublished journals of tours in various parts of the region in question, and to Mr. Nuttall's "Travels into the Arkansa Territory."

Compact Limestone.—We commence with the consideration of this stratum, as it is one of frequent occurrence, and perhaps occupies a greater extent of surface than any other. It so frequently alternates with the micaceous sandstones, and with the peculiar flint-rock of this district, that we have never been able to devise any theory of arrangement {301} which appeared applicable to more than an inconsiderable extent of territory.

A few miles west of the Rapids of the Canadian, a thin stratum of compact limestone, of the common blue variety, and abounding in organized remains, overlays the argillaceous sandstone of the coal formation. This limestone becomes more abundant towards the south, and is the prevailing rock on that part of Red river, near the confluence of the Kiamesha.[84] At Cape Girardeau, in the country a few miles in the rear of Herculaneum and St. Genevieve, and in many places throughout the district of the lead-mines, there is a coarse crystalline limestone, of a light gray colour, which is usually the lowest rock exposed in those places. It is very indistinctly stratified, and has in many respects a considerable resemblance to the more crystalline varieties of primitive limestone: for such it appears to have been mistaken by Mr. Schoolcraft, who, in his work on the lead-mines, asserts that the "mineral soil at Mine a Burton, and the numerous mines in its vicinity, reposes on primitive limestone," page 108. Afterwards, at page 119., speaking of this same primitive limestone, he says, "On going deeper, the rock again graduated into a compact limestone, very hard, and of a bluish gray colour, in which were frequently found small cavities studded over with minute pyramids of limpid quartz." And again, at the page first referred to, he informs us, "The primitive limestone passes into transition, and secondary, in various places on the banks of the Mississippi, between Cape Girardeau, and Saint Louis." We adduce these statements as confirming our own observations of the alternation of the crystalline or sparry limestone, with the compact blue variety; but as we have examined with great care several of the places mentioned by Mr. Schoolcraft, and many others apparently similar, we are disposed to think he has mistaken the character of the rock. We have never met with any {302} limestone about the lead-mines which did not contain organized remains; and the white crystalline variety abounds particularly in casts of encrinites, though these are not always manifest without careful examination.

This limestone, though rather indistinctly stratified, is marked by horizontal seams, distant one or two feet, and sometimes more, from each other. Its exposed surface becomes somewhat bleached and rough with small prominences, in which we may often distinctly trace the forms of animal remains. The recent fracture is uneven, distinctly crystalline, and much like that of many moderately fine-grained granites. Careful examination shows that in many instances the most minute particles visible under a lens, have assumed the rhombic form so common to the carbonate of lime. These crystalline particles vary greatly in size, and are sometimes half an inch across. In the interior of the casts of animal remains, they are sometimes less distinct than in parts of the rock where no such remains are discovered.

These vast beds of sparry limestone, made up almost exclusively of deposits from chymical solution, would seem to have been formed during periods when great tranquillity prevailed in the waters of the primeval ocean; and their alternation with limestones of the common earthy variety, and with sandstones made up of fragments rounded by attrition, may be considered as proofs that those periods, whatever may have been their distinguishing peculiarity, alternated with other periods of a different character.

This variety of limestone is perhaps the lowest rock hitherto noticed in the country of the lead-mines, and it may, according to the suggestion of Schoolcraft, be considered as the basis rock in that district; but as it certainly passes through every intermediate variety into the compact blue limestone, there seems to be no propriety in separating it from that rock, which often overlays the newest sandstones. If this view of the subject be admitted, it results that we are to consider {303} the whole of that part of the Ozark mountains which contains the lead-mines as belonging to a coal formation. We have met with nothing north of the Arkansa which appears to us to have any claim to be considered as belonging to the class of primitive rocks.

Mr. Schoolcraft informs us, that granite, gneiss, and mica slate exist in Missouri, but has omitted to point out the particular localities. See Views of the Lead Mines, page 92.

At St. Louis, Cote sans Dessein, Isle a Loutre, and at many points on the Missouri, the limestone partakes of the character of both the varieties above mentioned, but is rarely if ever so exclusively crystalline as in the lead-mine district. Most of the limestones between Franklin on the Missouri, and the Council bluffs, are distinctly crystalline, and are usually of a yellowish or reddish white colour.

The horizontal limestone near the mouth of the Ohio, is of a bluish gray colour, of a compact or fine granular structure, and contains some metallic ores often occurring in veins of beautifully crystallized fluat of lime. Near some of these localities of fluat of lime, we have observed the rock itself to contain small and apparently water-worn masses of hornstone, and some fragments of a perfectly white granular limestone.

Petrosilex.—In the vicinity of Bainbridge, ten miles above Cape Girardeau, is a stratified gray flint rock very similar in aspect, and having nearly a similar fracture to the common gun-flint. This rock is here an extensive stratum, and occurs in connection with compact limestone. In tracing it towards the south-west, we have not been able to detect the slightest interruption to its continuity through an extent of more than two hundred miles along the central portion of the mountainous district. Towards the south-west it is found to acquire gradually a more and more primitive character, and losing, near the Chattahoocke mountain the accompanying stratum {304} of compact limestone, it appears near the hot springs of the Washita, associated with the highly inclined argillite of that district. This rock, as far as our limited observations have extended, exhibits no traces of organized remains. Its colour seems gradually to change according to its age, or at least with the apparent age of the rocks associated with it. South of the Arkansa it is of a yellowish or pearly white colour; about White river, it is a dirty yellow, and at the St. Francis a grayish brown. A corresponding change may also be noticed in the inclination of the strata, and in other particulars. Aside from this apparently intimate connection there is a particular resemblance between the petrosilex of the Washita, and the flint rock of the lead-mine district. The rock in both instances falls readily into small masses of a few ounces weight. The hills it forms have usually a rounded outline, and often bear open forests of pine, while the timber on the sandstone hills is usually oak. Open woods of pine and oak occur in almost all the uplands in the Ozark mountains, and are considered unfailing indications of a meagre and flinty soil.

Argillaceous Sandstone.—The sandstones of this small group of mountains appear under almost every variety of character, but in most of them, as far as hitherto examined, we discover traces of coal or of those minerals and organized remains which usually accompany it. In the inclined sandstone near the hot springs, there are, it is true, no indications of coal; and that rock is in every respect similar to what are called the transition sandstones of the Alleghany and Coatskill mountains, but by following it an inconsiderable distance either east or west, it is found passing imperceptibly into the coal strata of the Poteau, and of the Little Red river of White river. In this instance, as in that of the stratum last mentioned, we find a rock apparently possessing as much unity as can belong to such a subject, passing from {305} recent secondary down, through all the intermediate grades, to the oldest transition, and thus heaping confusion upon our doctrines of the original continuity and systematic succession of strata.

A conspicuous character in the sandstones about the central and western portions of the region under consideration, is the great proportion of mica, in large scales, which enters into their composition. Fragments of the sand-rock, about the mouth of the Poteau, might be mistaken for mica slate. This mica is rarely if ever of that dark coloured variety which prevails in the Rocky Mountains; and in the other materials of these aggregates, there is a manifest want of resemblance to those mountains. A very slight comparison of the secondary formations at the base of the Rocky Mountains, with the similar aggregates in the Ozark range, will be sufficient to convince any one that they have resulted from the wearing down of primitive mountains, very dissimilar in character to each other.

We might have remarked, when speaking of the Rocky Mountains, the absence of any formation of talcose rocks, and indeed of magnesian fossils of any kind, and a corresponding deficiency of talcose and chloritic sandstones among the secondary rocks. We no sooner arrive at the western margin of the secondary belonging to the Ozark mountains, than we meet with extensive beds of sandstone, in which the prevalence of magnesia forms a conspicuous character. The beautiful argillaceous chlorite sandstone at the rapids of the Canadian, has been already described, and similar beds are not uncommon in many places in the vicinity of extensive depositions of coal.

Another peculiar variety of sandstone occurs, in connection with the sulphuret of lead, at the old mines of St. Michael, and at many places thereabouts. This bears apparently the same relation to the common sandstones, as the crystalline limestone above {306} mentioned does to the earthy varieties, and it alternates with and passes into the common rock in a similar manner. Its particles are crystalline, and appear to remain undisturbed in the position in which they were originally deposited from solution in water. Nevertheless the aggregate is manifestly secondary, and embraces the relics of many organized beings, as is common in the other secondary rocks.

There is also about the lead mines a sandstone composed of small glimmering grains of transparent quartz, and so loosely cemented as to fall rapidly to pieces, forming a light gray sand. In this variety we have sometimes observed the lead ore either disseminated, or forming horizontal veins between the laminÆ of sandstone. An examination of some spots might lead to the conclusion that the soil in which most of the lead has hitherto been found, has resulted from the disintegration of a sandstone of this kind.

Sandstone, though often covered at the surface by compact limestone or some other stratum is probably the rock which occurs in the greatest quantity throughout every part of this range of mountains. It is the prevailing stratum in all the country between the Arkansa and Red rivers, from the confluence of the Mamelle westward; rising to the height of two or three thousand feet, to form the summits of the Cavaniol, Sugar Loaf, and Mt. Cerne, and to a less considerable elevation at the Mamelle, Magasin, Caslete, and Short mountains.

North of the Arkansa it forms the body of the Chattahoocke mountain, and of many nameless elevations, which diversify the surface from the sources of the Little Red river to the Mississippi. Beds of coarse conglomerate or puddingstone, are met with in many places; but these are particularly frequent in connection with the inclined or transition sandstones about the Washita.

Native Argil.—Nine miles west of Bainbridge, on {307} the road to Jackson, and on the right bank of the Mississippi, near the head of Tiawapeti bottom, also in various other places in this vicinity, there are extensive beds of perfectly white native argil, of about the hardness of common chalk, for which it has often been mistaken.[85] See Schoolcraft's "Catalogue of Western Minerals," art. 1st. Notwithstanding Mr. Schoolcraft's confident assertion, it must yet be considered doubtful whether any chalk has ever been found in the region under consideration.

Specimens of the substance called chalk by the inhabitants, were collected at several places between Cape Girardeau and St. Louis. Also on the north side of the Missouri, on the road from St. Louis to Franklin. Some of these which were brought to New York, have been examined by my brother, Dr. J. James, and others, and were found to consist principally of argil, none of them occasioning the slightest effervescence with acids.

This substance, whatever it is to be considered, is distributed extensively throughout the country lying around the confluence of the Missouri and Mississippi. Some specimens have been sent from Illinois to the Lyceum of Natural History at Troy, where they are spoken of as a "littrographic carbonate of lime;" but whether any experiments have been made to ascertain their real character we have not been able to learn. We have not, from our own observation, found occasion to confirm the statement, that nodules of flint are found imbedded in this substance; but we have commonly found it accompanied by the flint rock already mentioned, which has in many respects a manifest resemblance to the flints occurring in chalk formation. We have sought in vain for the remains of echini and other animals so common in chalk beds.

Argillite.—Of the older secondary rocks, we have observed in the Ozark mountains only the inclined {308} sandstones and conglomerates above mentioned, and a limited formation of argillite, extending a few miles around the hot springs of Washita, and re-appearing on the Arkansa at and above the town of Little Rock, being usually accompanied by vast beds of petrosilex. This latter ought, perhaps, to be considered a distinct stratum, but south of the Arkansa we have not been able to trace it uninterrupted for any great distance.

Mr. Nuttall, in his valuable Journal of Travels into the Arkansa Territory, mentions grauwacke slate as occurring along the Arkansa river near Little Rock, p. 105. We have observed none here in any considerable degree similar to the grauwacke slate of the transition mountains of New York, or even to that of the Alleghanies. We are aware, however, that some of the aggregates which we call sandstones, have all the characters attributed to grauwacke slates, "grauwacke is a complete sandstone,"[86] and in a district where both are so intimately blended as in that we are considering, perhaps it is unnecessary to attempt any distinction between them; or we may persevere in the use of the two names at the same time, acknowledging they are both applied to the same stratum.

The hot springs of the Washita issue from clay-slate, and if we may judge from the inclination of the strata, and the distance at the surface from the granite of the cove, we may conclude a very large mass of clay-slate is interposed between the surface of the granite and the point at which the springs rise. This however it is not possible to ascertain. The hottest springs on the globe rise from beneath or within the granite,[87] and it is not improbable this rock may approach near the surface at many points {309} in the Ozark mountains, where it has not yet been uncovered.

The slate rock about the hot springs is highly inclined, often a good deal flinty in its composition, and as far as we have observed, contains no organised remains. It is traversed by large upright veins, filled usually with white quartz, contrasting strongly in colour with the dark blue of the slate-stone. The elevation of the "Hot Springs mountain" is estimated by Hunter and Dunbar at three hundred feet above the surface of the creek at the springs. This point is probably raised twenty or thirty feet above the Washita at Keisler. North of the springs the slate-rocks rise to greater elevation; but it is not probable that at any point where we have seen them, they attain the height of one thousand feet above the Mississippi.

The high lands between Washita and Red river are occupied principally by sandstone, the clay-slate appearing to extend from north-east to south-west, which, as far as we have observed, is the direction of the strata; these, when they are not perpendicular, usually dipping to the north-west.

The country about the sources of the Washita is represented as affording many interesting minerals; among them are enumerated "a martial pyrites, large bodies of crystallised spar, and hexagonal prisms, which are known to contain no small portion of the precious metals."[88] If the clay-slate in any part of this mountainous region should be found accompanied by its usual attendant, the metalliferous limestone, we should be more ready to credit the accounts of the precious metals being found, as at least some of the valuable mines in America exist in that stratum. But as yet we have no satisfactory accounts of the occurrence of that limestone, or any of the precious metals in that part of the United States.

{310} Granite.—About fifteen miles south-east from the hot springs, near the Washita, granite is found in situ. It forms the basis, and, as far as we could discover, the whole mass of a small hill, but little elevated above the level of the river; we found it emerging from beneath the soil at several parts of an area for two hundred or three hundred acres; but had not an opportunity to trace it to any great distance, nor to observe its connection with any other rock. The extent of surface which it covers, we believe, cannot be very great. This granite is very soft, and disintegrates rapidly when exposed to the air. It is compounded of grayish-white quartz, yellowish-white felspar, and an unusually large proportion of mica, in variously and brilliantly coloured masses. These large laminÆ of mica are white, pearl colour, yellow, brown, green, and often black, and in some instances are so large and numerous as to exceed in proportion the other ingredients of the aggregate. Talc also enters in large proportion into the composition of this granite. It is indeed sometimes so abundant as to occasion a doubt whether the whole should not be considered a bed of talc, rather than granite. This talc is in tabular masses, two or three inches in diameter, and about half an inch in thickness. Zeolite is also so abundant as sometimes to seem to take the place of the other materials of the granite. It is of two varieties, radiated and mealy. Stilbite (blaettriger zeolith of Werner) occurs in connexion with zeolith. The bed of one of the small streams which traverses this formation of granite is paved with small crystals of schorl, that of another with native magnet. Sulphuret of iron is disseminated in the granite. Several of the appearances presented by this interesting mass of granite, would seem to countenance the opinion that it is of secondary origin, like that mentioned by Saussure, as existing near the valley of Valorsine, at Semur en Auxois, and at the city of Lyons. In speaking of the granite {311} at these places, he says, "It could not be doubted on seeing these heaps of large crystals, that they are the produce of the rain-waters, which, passing through the granite, have dissolved and carried down these different elements, and have deposited them in these wide crevices, where they have formed new rocks of the same kind. The crystals of these new granites are larger than those of the ancient, on account of the repose which the waters enjoyed in the inside of these reservoirs."

The granite of the Washita, if it is to be considered as of secondary formation, appears to be much more extensive than any of the kind hitherto known. Many more particulars must, however, be ascertained before this question can be settled. We are ignorant of the manner of its connection with any other rock. Nor do we know of any formation of primitive granite from which it could, by the action of water, have been derived. One can have no hesitation, however, in considering the Ozark mountains, as a separate system within themselves, and having no immediate connection with the Alleghanies or Rocky Mountains. The sandstones which lie about these mountains, abound much more in mica than those near the Rocky Mountains, nearly in the same proportion as the granite of the latter has less than what is met with in the little we have seen of the former. The Ozark mountains exhibit evidence of metallic riches far exceeding any thing that appears in the Rocky Mountains. May not an extensive range of granite and other primitive rocks have existed at some distant period where the Ozark mountains now are, containing the vast quantities of the ores of lead, iron, &c. now found in rocks of recent secondary origin, and even in the alluvial? and may not the operations of water during many ages, when an ocean rolled over the summits of these mountains, have worn down those primitive rocks, their detritus having been deposited horizontally upon their submarine sides and summits; {312} so that the greater part of their surfaces are now covered by secondary aggregates? Our acquaintance with this range is however much too limited to admit of indulgence in such speculations.

Numerous specimens of minerals brought by Lieutenant Graham and Dr. Somerville from the Upper Mississippi and the Illinois rivers and others from that region, now in the possession of Dr. L. C. Beck, of St. Louis, have a peculiar resemblance to similar minerals met with in the Ozark mountains, south of the Missouri. From these resemblances, and the corroborating testimony of all the accounts we have received concerning that country, rich in mines, which lies along the eastern side of the Upper Mississippi, we have been induced to believe that a continuation of the Ozark mountains, or at least, of a region similar in Mineralogical features, extends from the confluence of the Missouri, northward to the sources of the Wisconsan, and the Ontonagon river of Lake Superior, north of the Missouri, the country is very little elevated; but aside from this it appears to possess all the peculiar features of the region we have been considering. The sandstones, the limestones, and other rocks, have a striking resemblance. Both regions abound in the ores of lead, and both afford copper.[89]

We are aware that the great irregularity in the direction of the ridges accessory to this range, and of the dip and inclination of the older secondary rocks belonging to it, may be considered objections to our idea of the connection and continuity of the different parts and the general direction of the group. But we are by no means anxious to maintain the position we have assumed. Our examinations have been limited, and we shall rejoice in any opportunity of correcting our errors, and enlarging our acquaintance with this interesting range of country.

{313} We subjoin in a note some account of a few of the most interesting minerals hitherto observed in connection with the rocks of this district.[90]

Recapitulation

The Ozark mountains extend from the sources of the Rio Colorado of Texas on the south-west, to the confluence of the Mississippi and Missouri on the north-east, and are continued in a low range from this point towards Lake Superior. They are widest in the south-west, and in that quarter they mingle with some low tracts of secondary sandstone, extending from near the Gulf of Mexico to the base of the easternmost ridge of the Rocky Mountains. Whether there is any similar expansion at the northern extremity, or whether this range is connected as a spur to the great primitive chain supposed to exist north of the great lakes, and is separated by a wide secondary and alluvial valley from the Rocky Mountains, is yet to be determined. This range consists of low ridges, irregular in direction, rarely rising to an elevation of more than 1500 or 2000 feet, and consisting principally of secondary rocks.

The strata are—

1st. Granite—at the cove of the Washita.

2d. Argillite—ranging north-east and south-west from Little Rock on the Arkansa to the hot springs, and thence to the sources of the Kiamesha.

3d. Transition Sandstone—a narrow margin, following nearly the same direction on the north-west side of the argillite, and usually inclining like it to the south or south-east.

4th. Flint (petrosilex)—From the hot springs north-east to the Mississippi, and usually forming the basis of the pine-lands.

5th. Limestone—Compact and sparry; distributed {314} in the same direction as the last, but more extensive.

6th. Argillaceous Sandstone—with extensive beds of coal, and abounding in mines of lead.

7th. Alluvial—There are many extensive tracts of deep argillaceous or calcareous loam; in other instances, a more meagre soil has resulted from the disintegration of the sand-rock.

These are the remarks we have been able, from observation, to make respecting the geology of a part of the United States' territory, west of the Mississippi. Relating to that part of the interior of our country which lies north-west of Lake Superior, and north of the sources of the Missouri, we have little satisfactory information. From the accurate and intelligent Mackenzie,[91] we are however able to collect a few important particulars. This enterprising voyager, it is well known, travelled from Montreal, L. C., in latitude 45° 30´, longitude 74°, in a north-west direction, to the mouth of Mackenzie's river, latitude 69°, longitude 135°; and again, at a later period, leaving his former route at the Lake of the Hills, about midway between Lake Superior and the mouth of Mackenzie's river, he ascended, in a south-west direction, the Unjegah, or River of Peace, to the Rocky Mountains, and crossing them, fell upon the sources of the northern branch of the Columbia, and from thence arrived at the Pacific, at a point a little north of the inlet of Queen Charlotte's sound. From him we learn that the Rocky Mountains continue in an uninterrupted chain, from the sources of the Missouri in the south, to a point beyond the sixty-fifth parallel of north latitude, near the mouth of Mackenzie's river. The River of Peace which he ascended in his journey to the western ocean, has its source in these mountains in about 55° north, nearly opposite to those of the great northern branch of the Columbia. Farther towards the south are the sources of the Saskatchawin, a large river, discharging itself from the {315} north-west into Lake Winnipic. The mountains in this part seem to be less elevated than those more to the south, but in other respects entirely similar. Their northern termination, according to this traveller, is in about north latitude 65°, 130° west longitude. Santa FÉ in New Mexico is in latitude 36°, longitude 104° 53´ west.[92] From this it will be perceived, that the general direction of this great mountain range is nearly from north-north-east to south-south-west. We have no evidence to confirm the conjecture, which, nevertheless, is highly probable, that the principal ridges of this range consist through their whole extent of granite or other primitive rocks. Considering the stupendous character, the great elevation and uniformity of the appearance of that portion of these primitive mountains with which we are acquainted, we should be led to look for similarity of character, and similar uniformity throughout. It is commonly believed, as asserted by Maclure, that "a large mass of primitive occupies all the northern part of this continent;" and he considers the great Atlantic range of primitive, the mountains of New England, New York, and the Alleghanies, as a spur for this formation. We are not acquainted with the grounds on which this opinion is founded, but we see no reason to consider it an improbable one. Of the northern boundary of that vast formation of secondary which certainly occupies a very large portion of the interior of this continent, we are ignorant. On the south-east, its limit is the irregular border of the transition of the Alleghanies, commencing between the Alabama and Tombigbee rivers, and running north-west to Fort Anne, near Lake Champlain. From this point, a narrow and perhaps interrupted strip of secondary extends through the valley of Lake Champlain to the upper parts of St. John's river. The island and mountain of Montreal are of secondary. The country {316} also between St. John's and La Prairie is most probably secondary, as is much of that along the St. Lawrence below Montreal. From the termination of the transition near the confluence of the Alabama and Tombigbee, the secondary rocks continue on the south-west, sometimes concealed by the recent alluvial to the Black-lake river, near Natchitoches. Beyond this, the information we have is not satisfactory. From this point, turning north-west, we may for the present consider the Red river of Louisiana as the boundary of the secondary, or rather the limit of our acquaintance with this formation.

Beyond the Ozark mountains, the district between the Red river and the Canadian is occupied by the red sandstone of the salt formation, mentioned when speaking of that region, and is undoubtedly to be considered secondary. How far it extends to the west beyond the sources of Red river and the Canadian, we are unable to determine. At the commencement of the most eastern ridge of the Rocky Mountains, a few south of the high peak, and at no very great distance north from Santa FÉ, the boundary again becomes determinate. From this point it runs nearly north one hundred and fifty miles, where it crosses the river Platte. From the narrative of Lewis and Clarke, we are enabled to determine with sufficient accuracy, that it crosses the Missouri not far from the Falls, in longitude 110° west. Beyond this, the little information we have, we owe to Sir Alexander Mackenzie. He informs us, that great quantities of pit coal are found about the sources of the Saskatchawin which lie near the Rocky Mountains, and between 50° and 55° north latitude. The sources of Saskatchawin are placed by this traveller near the base of the Rocky Mountains; and the coal formation which he mentions, lies on the margin of a plain extending far to the north and east. The Saskatchawin running to the east, traverses 15° of longitude, and discharges its waters into Lake Winnipic in {317} latitude 53° north. Lake Winnipic is connected by the Severn and Port Nelson rivers to Hudson's-bay. There is a water communication, interrupted by one portage, from the Saskatchawin, north-west, to the Mississippi or Churchill's river; and from thence, by the Lake of the Hills, Slave Lake, and Mackenzie's river, to the North Sea. Near the Lake of the Hills, in latitude 59°, Mackenzie found several brine springs. This, though not decisive evidence, perhaps justifies the conclusion, that secondary rocks exist in that neighbourhood. A view of the character and direction of the several large rivers which traverse the region about Hudson's Bay, of their numerous inosculations, and the number and position of the small lakes which abound in every part of it, afford, at least, presumptive evidence, that it is an extensive plain little inclined in any direction.

We may, perhaps, venture to conclude, that the secondary formation extends uninterrupted along the base of the Rocky Mountains, as far as to the Saskatchawin, where coal was observed by Mackenzie. What lies beyond is as yet unknown. From this coal formation, our boundary must for the present run in a direction a little south of east to Lake Superior, whence it may, with a few inconsiderable interruptions, follow the territorial boundary of the United States, until it arrives at 45° parallel of latitude, thence by the St. Lawrence to Montreal. The slight acquaintance we have with the country north of this line, is perhaps insufficient to justify the conjecture, that secondary formations occupy an extensive portion of that country. It is improbable, that formations of secondary extend along the base of the Rocky Mountains through their whole course, and from thence spread themselves to the east, knowing no limits but Atlantic mountains, the shores of the Gulf of St. Lawrence, and the northern ocean. We know that rocks of this formation exist about the {318} Gulf of St. Lawrence, whence coal, plaster, and sandstone, are brought to our markets.[93]

This boundary of the great formation of secondary rocks, which occupies so large a portion of the interior of our continent, includes a vast area of surface, extending through 25° of latitude, and 60° of longitude. I intend to consider that portion of it only of which the state of facts at present known enables us to speak with some degree of confidence. This portion may be conceived as occupying the area of a large triangle, the base of which is a line running from Montreal in Lower Canada, south-west to a point, near the outlet of the river Sabine, the western boundary of the state of Louisiana. The summit would be at the sources of the Saskatchawin, which are west of north from the mouth of the Sabine, and north of west from Montreal. The Rocky Mountains on the west, and the Alleghanies on the south-east mark the limits of the secondary in those directions. Its extent towards the north and north-east is as yet unknown.

In the wide space included within the lines above mentioned, we know of but one exception to the remark, that all the rocks found in place are secondary. This is the instance of the Ozark hills traversing the horizontal strata from south-west to north-east, somewhat in the manner of a whindyke. The most striking peculiarity of this range, is the prevalence among the secondary strata of crystalline substances, and what are called rocks of chymical deposition, and the alternation of these with beds and strata whose integrant particles bear evident marks of having been worn and rounded by mechanical attrition. {319} Appearances of this kind are observed in all formations of secondary rocks, but it is believed, are, in few instances, as extensive or as numerous as in this. It is well known, that the ores of lead, so abundant in many parts of this range, occur in the uppermost strata of horizontal sandstone, or in primary soils superimposed upon those sandstones. It has been suggested, that these ores of lead may have been brought down in the alluvion of rivers from some more ancient and elevated region, but any one who shall examine them in connection with the substances with which they are now found associated, will, we think, be convinced of their having been of contemporaneous origin with the sandstone. That the sparry limestones, the crystalline sandstones, and perhaps the ores of lead, (almost invariably found in the form of crystals,) have been deposited from solution in water, is highly probable; and that these depositions must have taken place in connection with circumstances not unfavourable to animal life is evident, as all these crystalline rocks abound in organised remains.

In attempting an explanation of these appearances, can any assistance be derived from recourse to the ingenious suggestion of Bakewell, that the matter of these crystalline beds and strata has been ejected from beneath the crust of the earth in a state of chymical solution. These submarine eruptions may have been numerous, and may have happened at different and remote periods; hence the alternation of rocks, consisting of particles mechanically aggregated together with those of chymical deposition. Hence the existence of metallic ores overlaying recent marine sandstones and compact limestones; for these ores, in a state of solution, may have been the matter thrown out in some of the latest eruptions.

This supposition may derive some confirmation from the well known fact that this region is still in a remarkable degree subject to subterranean concussions {320} and earthquakes. These concussions centring apparently in this range of mountains, and felt at times throughout all the western parts of the United States, are certainly too considerable in force and extent to be attributed to the operation of a cause so limited and superficial as the decomposition of beds of lignite lodged among the alluvion of the Mississippi. We do not insist upon the accounts that have been so often circulated, of the blowing, smoking, and burning mountains, said to exist in the country west of the hot springs of the Washita, because these accounts want confirmation.

Though this range of mountains has probably a nucleus of primitive rocks running through its whole extent: yet these appear but rarely at the surface. We have seen such only in the places already mentioned, and have been informed of others in Washington county, near the sources of the St. Francis, and about Lake Superior.[94]

From the information we have been able to collect, we are induced to believe that secondary rocks occupy the country on both sides of Red river, from its sources to its confluence with the Mississippi. If this be the case, the primitive of the Ozark mountains must be considered a small and insulated mass.

The inequalities of surface in this great secondary formation are considerable. It has often been called the "basin of the Mississippi," but with little propriety, since it might with equal accuracy be called the basin of the St. Lawrence, the Saskatchawin or Mackenzie's river. The form of that part of it which contains the Mississippi, is however similar to that designated by geologists as a basin-shaped cavity. As far as our acquaintance extends, it is bounded on all sides, except a narrow space at the outlet of the Mississippi, by a surface of greater elevation than itself. But whether this surface is not sometimes of secondary {321} formation is doubtful. It is dangerous to infer the existence at a former period of an insulated inland sea from any formation of secondary rocks, without being acquainted with its whole extent, with its elevation at different points, and its connexion with other rocks. On the south-east, secondary sandstones and depositions of coal are met with in some of the most elevated parts of the Alleghany mountains. The positive elevation of the primitive mountains of New England is, except at a few points, scarce equal to that of the secondary in the western parts of the state of New York. From the primitive rocks near Philadelphia, to the secondary of the Alleghanies, is an almost uninterrupted ascent. The clay-slate and granite of the Washita, occupy nearly the lowest part of the surface of the Mississippi valley. We are as yet destitute of barometrical or other observations, by which we might determine the actual height which the secondary rocks reach on the sides of the Rocky Mountains. Pike estimates the elevation of the plain at the foot of the mountains, at 8000 feet above the level of the ocean. This is doubtless overrated. We have already observed, that secondary rocks are found upon the sides of the Rocky Mountains, considerably above the level of the plain. It is probable, that this estimate of Pike's far exceeds the truth, yet any one who considers the great length and rapidity of the rivers which flow from that region, the severity of cold in winter, the rapidity with which evaporation is carried on in summer, the transparency and peculiar aspect of the sky, will be convinced that those tracts are highly elevated; and there is unquestionably good reason to believe, the secondary rocks along the eastern base of the Rocky Mountains have in many points an elevation at least equal to the summits of the Alleghanies.

This vast formation of secondary, extending as it probably does from the Gulf of Mexico to the Northern ocean, and from the Bay of St. Lawrence {322} to the Rocky Mountains, must of necessity occupy in various parts different and sometimes great elevations: like other great fields of the same formation, its borders are marked by high and broken ridges, which become less elevated and less frequent towards the centre. Sandstone appears to be the basis and predominating rock occupying the borders contiguous to the primitive and transition, and passing under the more recent secondary. In this sandstone on the outskirts of the secondary, have been found most of the extensive coal beds hitherto known, also gypsum and brine springs.

Horizontally stratified limestone is met with in many parts of this formation, but is most abundant in the central portions, about the beds of the great rivers, and in those parts which have the least positive elevation. Compact limestone is a name sometimes used to designate all the varieties of that rock occurring in districts of secondary, but is certainly inapplicable to the limestone about Cape Girardeau and in many other places, which is notwithstanding manifestly secondary. Some of the limestone north-west of the primitive on Hudson's river, about the Coatskill and Hellebergh mountains, is of this crystalline variety, but abounds in marine exuviÆ. That of Lake Champlain, as well as the greater part of that in the interior and western parts of the state of New York, is of the compact blue variety. From the falls of the Ohio at Louisville to Cincinnati, a mixed kind, partaking of the character of both of the before-mentioned varieties, is found along the river, and for some distance on each side. From Dr. Drake we learn, that this limestone is confined to a small district, and is on all sides bounded by sandstone, which rises from below it, and on which it is supposed invariably to rest. Whether the red sand-rock which is found on the south-west branches of the Arkansa, in a horizontal position, and in an highly inclined one skirts the Rocky Mountains, {323} extends to other parts of this formation of secondary, we are unable to say.

Throughout the country adjacent to the Ohio river, the prevailing and basis rock is a gray horizontal sandstone, often approaching in character those varieties which contain coal. It embraces extensive beds of coarse conglomerate, and supports or alternates with compact limestone.

Of the Alleghany Mountains

By this name we intend to designate the great range of mountains extending parallel to the Atlantic coast, from the sources of the St. John's river in New Brunswick in the north-east, to the confluence of the Alabama and Tombigbee in the south-west. An outline of this great chain has already been traced by Maclure, and particular accounts of portions of it are to be found in the works of Eaton and others; we shall, therefore, confine our attention to those strata, which, forming the north-western side of the range, are most intimately connected with the great secondary formations of the west.

1st. Granular Limestone—Appears in every part of the United States, where it has hitherto been observed to be the uppermost in the series of primitive rocks. It is true, it is often found to graduate, by minute and imperceptible shades of difference, into that which is decidedly secondary. Instances of this have been observed so frequently that the fact can be no longer questioned. This fact, and others of the same kind, ought not, perhaps, to be considered as invalidating the received opinions with regard to the classification of rocks according to the doctrines of Werner. If a division is to be made of the rocky strata of the earth into primitive, transition, &c. it is, perhaps, of little importance whether the boundaries thus instituted shall traverse beds of the same substance, {324} or separate contiguous strata composed of different materials.

That series of rocks next in order to the primitive limestone above mentioned, has been very generally denominated the Transition Class. It comprehends the following strata: Metalliferous limestone, Clay-slate, Graywacke, and Graywacke-slate, and Old Red sandstone. If we confine our attention to the consideration of these rocks as they exist in our own country, we shall find them appearing in their different localities under circumstances of considerable uniformity.

2d. Metalliferous Limestone.—The prevailing colour of this rock is blue, of various shades and intensities, varying into yellow and gray. It has usually a close texture, an even, large conchoidal, or somewhat splintery fracture. In many varieties the surface, by long exposure, becomes coated with an incrustation of a yellowish white powdery matter, which adheres closely. It is frequently traversed by small reticulating veins of quartz or calcareous spar, which, during the gradual decomposition of detached masses, resist the progress of disintegration, and are left standing out from the surface, giving it a chequered appearance. It is the lowest and is considered as the most ancient of the rocks containing organized remains, which are those of cryptogamous plants, and animals without sight.

Geographical distribution.—This rock occurs extensively along all the north-western side of the primitive of the great chain of the Alleghanies. In lower Canada and Vermont, it is accompanied by granular limestone and granular quartz, which separate it from the mica slate and talcose rocks on the east. [See Eaton's Index to the Geology of the Northern States.] It is there usually inclined towards the west, at an inconsiderable angle. It is separated from the compact fletz limestone of the valley of Lake Champlain by a stratum of old red sandstone, which forms {325} the upper part of a range of hills, called, in Vermont, the Snake mountain. In Berkshire county, in the western part of Massachusetts, and along the eastern side of the Hudson in New York, a stratum of primitive clay-slate intervenes between this rock and the granular limestone. The New Lebanon mountain, which is of slate, and divides the primitive limestone of Pittsfield, Richmond, Stockbridge, &c. from the transition which occurs at New Lebanon springs, and along the western base of this range, is considered primitive. (Dewey in Silliman's Journal.) To the north-east of the Hudson river, the transition limestone nowhere occupies any great extent of surface from east to west, but is a narrow strip running along the margin of the primitive, and in a few miles is succeeded either by red sandstone, or clay-slate resting upon it. In Vermont, in the same neighbourhood, it alternates with clay-slate, and supports red sandstone.

Crossing the Hudson above the highlands, and proceeding south-west, little of this stratum is seen in the lower part of New York; but it becomes more abundant in the western parts of New Jersey and Pennsylvania. If we suppose the whole of the Alleghany mountains of Pennsylvania, Maryland, and the western parts of Virginia, removed to a level with the surface at base of their eastern declivities, it is probable their foundation, which would be thus exposed, would be found through their whole extent to be of transition limestone. This rock is almost the only one which occurs between the primitive limestone. About twenty miles west of Philadelphia and Harrisburgh, Cove Hill, the North and South mountains, and the other eastern ranges of the Alleghany, are all based upon metalliferous limestone. It is seen emerging from beneath the sandstone which forms the body of these mountains at O'Connel's town, and in most of the vallies between the Alleghanies. We learn from Maclure, that it extends itself to the south and west, nearly to the termination of this range of mountains at the {326} confluence of the Alabama and Tombigbee rivers in Mississippi.

3d. Transition Argillite.—This name is intended to comprehend not only the common varieties of the clay-slate of transition, but also some varieties of graywacke, and the siliceous slate by some considered a distinct stratum. It is believed, that throughout the range of country occupied by the several rocks here mentioned, they will be found too intimately blended, and too closely entangled with each other, to allow of their being considered as separate formations.

Geographical distribution.—The formation including the above mentioned rocks, may with propriety be denominated clay-slate of transition. As far as our acquaintance has extended, it occurs in all its localities associated with metalliferous limestone, or old red sandstone. It is not to be confounded with the primitive argillite which occurs below transition limestone, and is met with in the highly primitive parts of New England, nor with the aluminous schist of the great secondary formation to the west. It is distinct from either; and in most instances its character is marked with sufficient distinctness. It occurs in the central portions of that extensive field of transition which skirts the western margin of the primitive of New York and New England, and forms the great body of the Alleghany and Catskill mountains. It is wider and more extensive in the north, occupying much of the surface in Vermont, the northern parts of the state of New York and Canada. In the Alleghany mountains of Pennsylvania, Maryland, and Virginia, its beds are of great thickness, and form, in some instances, the prevailing rocks, being, however almost invariably overlaid by sandstone. It has, in several instances, been observed to contain impressions of organized remains, but these are usually those of zoophytic animals, and are exceedingly unlike those found so abundantly in the schist of coal formations. Its colours are variable, it {327} is, however, most commonly blueish, black, or dark brown. Between Albany and Pittsfield, it is met with of a green colour, and a few miles to the south-east of White-hall, New York, it is bright red.

The graywacke, which in this very general and hasty view we have considered as in part belonging to the clay-slate of transition, appears to us to form the connecting link between that clay-slate and the old red sandstone. In attempting to give a more detailed account of these formations, we might perhaps speak of the graywacke as others have done, as a distinct stratum. We have, however, usually found it so intimately blended either with the sandstone or clay-slate, that in this enlarged view we see no necessity for a separation. We cannot agree in opinion with some who have considered the graywacke as the substratum of the great secondary formation of the valley of the Mississippi. We have found it almost invariably overlaid by an inclined sandstone, separating it from the secondary rocks towards the west. This may not be as often the case at the north, as in Pennsylvania, Maryland, and Virginia. Mr. Eaton is of opinion, that "graywacke underlays all that district of country in the interior of the state of New York, which would be bounded on the north by a line drawn from Albany westward to the Onondaga salt springs; on the west, by a line running from the salt springs by Bath to the Pennsylvania line; on the south, by a line running thence to Newbergh on the Hudson, above the highlands; and from thence to Albany, by a line running parallel to the river, at a few miles distance." We are informed by Governor Clinton,[95] that coal strata exist in the western part of the state of New York, and we are induced from the analogy of the other parts of the same great secondary formation, to believe that the brine springs of Onondaga rise not from graywacke, {328} but from the sandstone of that coal formation. According to Maclure,[96] old red sandstone appears from under the limestone and other strata at Lewestown, ten miles below the falls of Niagara, and also near the salines of Onondaga in Genessee county. "This," says he, "would give some probability to the conjecture that the old red sandstone is the foundation of all this horizontal formation, and is perhaps attached to some series of rocks laying on the primitive north of the Great Lakes."

Sandstone of Transition. Old Red Sandstone of Werner?—Throughout the whole extent of the transition formation before mentioned, a sandstone occurs, evidently belonging to the oldest depositions of that rock. It is for the most part distinctly stratified, and in all cases its stratifications are inclined. It consists of grains of quartz, united by a scanty cement, and usually more or less rounded, as if by attrition and the operation of currents of water. Their fragments vary in magnitude from the finest sand to boulders of several pounds weight. Among the Alleghany mountains are many extensive beds of puddingstone or coarse conglomerate, usually coloured by oxide of iron. It is also to be observed, that this formation of transition sandstone sometimes embraces extensive beds, whose integrant particles have by no means the appearance of having been rounded by attrition. As in the case of almost all the rocks of secondary formation, there appear to have been periods during the time of its deposition when the waters of the superincumbent ocean ceased to throw down the mechanical dÉbris of former rocks, and deposited earthy matter from a state of chymical solution. It is perhaps one of the most interesting and most difficult problems which remain unsolved, to account for the alternation through the whole series of lower secondary and fletz rocks, of {329} beds of strata of mechanical with those of chymical deposition.

The Alleghany mountains in New York, Pennsylvania, Maryland, and Virginia, are made up principally of rocks belonging to the transition class, and among these sandstone is perhaps of more frequent occurrence than any other aggregate. We are aware that Maclure has not considered the sandstones of the Alleghany mountains generally, as belonging to the old red sandstone formation of Werner; and it must be acknowledged there is some difference, at least in colour, between the ferruginous sand-rock, which commences on the shore of Tappan bay near Nyac, and extends south and west by the way of Newark, Amboy, and Brunswick, in New Jersey, and that which forms the body of the Cove, Sideling and Alleghany ridges farther to the west. But we cannot discover so marked a difference between the sandstone of the localities last mentioned, and that which occurs about the South mountain in Pennsylvania, that at Hagerstown in Maryland, and near Harper's ferry, in Virginia, which Maclure considers as the old red sandstone. Indeed, this last appears to us in almost every respect to resemble the inclined sandstone which prevails so generally throughout the middle and eastern ridges of the Alleghany mountains in Pennsylvania and Maryland. We have already stated the opinion, in part sanctioned by the observations of Maclure, that the old red sandstone is the great substratum of the part of the secondary formation south of Lake Ontario. If this be the case, what stratum, if not the old red sandstone, should be seen emerging from beneath that secondary along its south-eastern margin? We will not, however, contend for the name. It is sufficient for our purpose to state, that the sandstone so abundant in all the principal ridges accessory to the Alleghany on the east, has the character of a rock belonging to the transition class of the Wernerians; that is, its {330} strata have a somewhat regular dip and inclination; it contains no beds of bituminous coal, though many of anthracite, and few organised remains. Near the summit of the ridge called particularly the Alleghany, the change to secondary begins to appear. Without the interposition of any other stratum, and without any sudden change of features, the strata of sandstone become nearly horizontal, assuming gradually all the characters of secondary rocks. About one mile west of the summit of the Alleghany, on the road from Philadelphia to Pittsburgh, the first indications of coal are observed. Descending into the vallies, the transition strata again emerge to the light. The same thing happens in the case of Coatskill and other mountains west of the Hudson, their basis being of transition, and their summits crossed with secondary.

The horizontal sandstones connected with the depositions of coal occurring along the Ohio from Pittsburgh to the confluence of Green river, assume various characters,[97] and often support extensive formations of compact limestone.