NIAGARA FALLS A CLOCK OF RECENT GEOLOGICAL TIME

Features in and about the Niagara gorge.—A striking example of those permanent alterations of drainage which have resulted from the presence of the late continental glacier in North America is to be found in the Niagara gorge between Lakes Erie and Ontario. With the aid of borings many of the now buried channels of the region have been followed out, and in a later paragraph we shall refer to some of the stronger lines of the earlier drainage system. Before undertaking the study of Niagara history, it is essential that one become somewhat familiar with the present topography in and about the Niagara gorge.

Below the present cataract the river flows through a deep gorge for about seven miles before issuing at the Lewiston Escarpment (Fig. 381, p. 355). This gorge has been cut in beds of rock sediments which dip at a gentle angle southward toward Lake Erie. The capping of the rock series is a compact and relatively resistant limestone which is known as the Niagara limestone, beneath which there are alternating beds of shale with thinner limestone and sandstone. The plain formed by the upper surface of the limestone capping terminates in the Lewiston Escarpment, which is transverse to the direction of the gorge and seven miles distant below the Falls. The depth of the gorge varies markedly, the above-water portion being represented at the upper end by the height of the cataract, one hundred and sixty-five feet, while at its lower end near Lewiston it is twice that amount. Halfway down the gorge a sharp turn is made at an angle of more than ninety degrees, and the upstream arm is extended to form a basin which contains the famous whirlpool. This visible extension of the upper gorge is continued in a buried channel, the St. Davids Gorge, which extends to the escarpment, broadening as it does so in the form of a trumpet. The materials which fill this earlier channel are notably coarse glacial deposits (Fig. 389).

Directly above the whirlpool the Niagara gorge is first contracted, but almost immediately swells out into the form of a sausage, which under the name of the Eddy Basin extends to the constricted channel occupied by the Whirlpool Rapids. This Gorge of the Whirlpool Rapids extends to and a little above the railroad bridges, where it again suddenly widens and deepens and with surprisingly uniform cross section now continues as far as the cataract. This uppermost section is known as the Upper Great Gorge. About a mile below the whirlpool is that remarkable projection into the gorge from the Canadian wall which is known as Wintergreen Flats, below which and nearer the river are Fosters Flats. Almost throughout its entire length the Niagara gorge is bordered on either side by a narrow and gently incurving terrace eroded below the general level of the plain and meeting the gorge in a sharp angle (Fig. 377).

The features immediately about the cataract show that the Falls are to-day in a condition which, so far as we know, has occurred but once before in their entire history—the waters of the river are divided unequally by an island, and for this reason, as we shall see, the cataract enters over the side wall of the gorge instead of at its end (Fig. 381), although the turning of the channel from this cause is combined with a bend of the river.

The drilling of the gorge.—There appear to be two important processes which are responsible for the recession of the Falls, the rate of which is determined largely by the resistance of the limestone capping and the tenacity of the looser shale beneath it. One of the eroding processes operates from below and undermines the cap until the unsupported cornice falls in blocks to the bottom of the gorge; the other makes its attack directly from above, selecting for the purpose the lines of jointing of the rock which it widens by solution and corrasion until the included blocks are in so far separated that they are torn out and go over the brink of the Falls (Fig. 378). This process of overhead attack in the powerful currents just above a cataract is even better illustrated by the Falls of St. Anthony near Minneapolis, which have had a similar history of recession to that of the Niagara Falls (Fig. 379).

The blocks of the capping limestone at Niagara Falls are to some extent fixed in size by the joint planes present in them, and as they fall to the bottom of the gorge, they promote or retard the further recession of the Falls according as they can or cannot be moved about by the churning currents beneath the cataract. Of the retarding effect there is an illustration in the accumulation of the blocks below the American and the intermediate Luna Falls (plate 23 A), which the weaker currents upon the American side find too heavy to handle.

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The Canadian Fall, with its much greater power, is an example of the promotion of recession through the churning about of the blocks at the base of the cataract. We have here to do with a churn drill which bores its way into the bottom of the gorge with increasing radius of rotary motion with each increase in volume of the falling water. Under this rotary churning the soft shales are torn out near the bottom and in succession the harder layers above until the capping is reached (Fig. 380). The conditions appear now to be such that the effective work is largely concentrated, as it usually has been, near the middle of the channel; and so the gorge recedes with a margin of the earlier river bed remaining as a terrace on either side and extending to the former river bank (Fig. 377).

As must have been noted, one peculiarity of the operation of the churn drill beneath the cataract is that the depth of the gorge will bear a direct proportion to its width, and if the volume of water has varied during the process of recession, these changes in volume will be registered in the width and also in the depth of that section of the gorge which was drilled at the time—the cross section of the gorge at any place is proportional to the volume of the water falling in the cataract which produced it, modified, however, by the competency to handle the joint blocks of definite size (Fig. 381).

The present rate of recession.—There are various sketches, more or less accurate, made in the early part of the nineteenth century, and from the later period there are daguerreotypes, photographs, and maps, which refer especially to the Canadian Fall; and which, taken together, render possible a comparison of the earlier with the later brinks. By comparing the earliest with the recent, views it is seen at a glance that the Falls are receding, and at a quite appreciable rate (Fig. 382). A careful comparison of the maps made in 1842, 1875, 1886, 1890, and 1905 of the brink of the Canadian Fall (Fig. 383) indicates that for the period covered the rate of recession has been about five feet per year, and similar studies made of the American Fall show that it has been receding at the rate of only three inches per year, or one twentieth the rate of the recession of the Canadian Fall.

Future extinction of the American Fall.—It is because of this many times more rapid recession of the Canadian Fall that the Niagara cataract, instead of lying athwart the gorge, enters it from its side. The Canadian Fall is thus in reality swinging about the American, and the time can already be roughly estimated when this more effective drilling tool will have brought about a capture, so to speak, of the American Fall through the cutting off of its water supply. It will then be drained and left literally “high and dry”, an enduring witness to the geological effect of an island in making an unequal division of the waters for the work of two cataracts.

As already pointed out, the inefficiency of the American Fall as an eroding agent is amply attested by the wall of blocks already appearing above the water below it. The tourist who a thousand years hence pays a visit to the Niagara cataract, provided the water flow is allowed to remain as it has been, will find above this rampart of blocks a bare cliff in part undermined, and surmounted by a nearly flat table surface which is cut off from the existing cataract by a higher section of the gorge (Fig. 384). It is quite likely that this table will furnish the most satisfactory viewpoint of the future cataract of that date.

The captured Canadian Fall at Wintergreen Flats.—What we have predicted for the future of the present American Fall will be the better understood from the study of a monument to earlier capture made long before the upper section of the gorge had been cut or the whirlpool had come into existence. The tables were then turned, for it was a fall upon the Canadian side of the gorge that was captured by one upon the American. The locality is known as Wintergreen Flats, or sometimes as Fosters Flats; though the first name properly applies to a higher surface near the brink of the gorge, and Fosters Flats to a lower plain near the level of the river (see Fig. 381, p. 355). The peculiar topographic features at this locality are well brought out in Gilbert’s bird’s-eye view of the locality (Fig. 385); in fact, in some respects better than they appear to the tourist upon the ground, for the reason that the abandoned channel and the Flats on the site of the since undermined island are both heavily forested and so not easy to include in a single view. For one who has studied the existing cataract this early monument is full of meaning. Standing, as one may, upon the very brink of the former cataract, it is easy to call up in imagination the grandeur of the earlier surroundings and to hear the thunder of the falling water. A particularly vivid touch is added when, in digging over the sand about the great blocks of fallen limestone underneath the brink, one comes upon the shells of an animal still living in the Niagara River, though only in the continual spray beneath the cataract.

The Whirlpool Basin excavated from the St. Davids Gorge.—It has already been pointed out that a rock channel now filled with glacial deposits extends from the Whirlpool Basin to the edge of the escarpment at St. Davids (Fig. 389, p. 363). In plan this buried gorge has a trumpet form, being more than two miles wide at its mouth and narrowing to the width of the upper gorge before it has reached the Whirlpool. Near the Whirlpool it has been in part excavated by Bowman Creek, thus revealing walls that are well glaciated. Different opinions have been expressed concerning the origin of this channel, one being that it is the course either of a preglacial river or one incised between consecutive glacial invasions; and another that it is a cataract gorge drilled out between glacial invasions after the manner of the later Niagara gorge. In either case its contours have been much modified by the later glacier or glaciers, whose work of planing, polishing, and widening is revealed in the exposed surfaces; and it is not improbable that a cataract has receded along the course of an earlier river valley.

As we shall see, there are facts which point rather clearly to an earlier cataract which ended its life immediately above the present Whirlpool. When the later Niagara cataract had receded to near the upper end of the Cove section, or near the present Whirlpool, the falling water must have been separated from this older channel and its filling of till deposits by only a thin wall of rock, and this must have been constantly weakened as its thickness was further reduced.

When this weakened dam at last gave way, it must have produced a debacle grand in the extreme. It is hardly to be conceived that the “washout” of the ancient channel to form the Whirlpool Basin could have occupied more than a small fraction of a day, though it is highly probable that the broken rock partition below the Whirlpool was not immediately removed entire. The mandible-like termination of the Eddy Basin immediately above the Whirlpool has led Taylor to believe that the cataract quickly reËstablished itself at this point upon the last site of the extinct St. Davids cataract. If reduced in power for a short interval, as a result of the obstructions still remaining in the lately broken dam below the Whirlpool, the remarkable narrowing of the gorge at this point would be sufficiently accounted for.

Being compelled to turn through more than a right angle after it enters the Whirlpool Basin, the swift current of the Niagara River is forced to double upon itself against the opposite bank and dive below the incoming current before emerging into the Cove section below the Whirlpool (Fig. 386).

In tearing out the loose deposits which had filled this part of the buried St. Davids Gorge, many bowlders of great size were left which slid down the slope and in time produced an armor about the looser deposits beneath, so as to protect them and prevent continued excavation. Thus it is found that the submerged northwestern wall of the basin is sheathed with bowlders large enough to retain their positions and so stop a natural process of placer outwashing upon a gigantic scale (Fig. 386).

The shaping of the Lewiston Escarpment.—To understand the formation of the Lewiston Escarpment cut in the hard Niagara limestone, it is necessary to consider the geology of a much larger area—that of the Great Lakes region as a whole. To the north of the Lakes in Canada is found a most ancient continent which was in existence when all the area to the southward lay below the waters of the ocean. In a period still very many times as long ago as the events we have under discussion, there were laid down off the shore of this oldland a series of unconsolidated deposits which, hardened in the course of time, and elevated, are now represented by the shales, sandstone, and limestone which we find, one above the other, in the Niagara gorge in the order in which they were laid down upon the ocean floor. The formations represented in the gorge are but a part of the entire series, for other higher members are represented by rocks about Lake Erie and even farther to the southward. These strata, having been formed upon an outward sloping sea floor, had a small initial dip to the southward, and this has been probably increased by subsequent uptilt, including the latest which we have so recently had under discussion. At the present time the beds dip southward by an angle of less than four degrees, or about thirty-five feet in each mile.

When the elevation of the land in the vicinity of this shore had caused a recession of the waters, there was formed a coastal plain on the borders of the oldland like that which is now found upon our Atlantic border between the Appalachians and the sea (Fig. 272, p. 246). The rivers from the oldland cut their way in narrow trenches across the newland, and because of the harder limestone formations, their tributaries gradually became diverted from their earlier courses until they entered the trunk stream nearly at right angles and produced the type of drainage network which is called “trellis drainage.” It is characteristic of this drainage that few tributaries of the second order will flow up the natural slope of the beds, but on the contrary these natural slopes are followed in the softer rock nearly at right angles again to the tributaries of the first order of magnitude (Fig. 387). Thus are produced a series of more or less parallel escarpments formed in the harder rock and having at their base a lowland which rises gradually in the direction of the oldland until a new escarpment is reached in the next lower of the hard formations. Such flat-topped uplands in series with intermediate lowlands and separated by sharp escarpments are known as cuestas (see p. 246), and the Lewiston Escarpment limits that formed in Niagara limestone (Figs. 387 and 388).

Episodes of Niagara’s history and their correlation with those of the Glacial Lakes.—Of the early episodes of Niagara’s history, our knowledge is not as perfect as we could desire, but the later events are fully and trustworthily recorded. The birth of the Falls is to be dated at the time when the ice front had here first retired into what is now Canadian territory, thus for the first time allowing the waters from the Erie basin to discharge over the Lewiston Escarpment into the basin of the newly formed Lake Iroquois (Fig. 364, p. 334). Since the level of Lake Iroquois was far above that of the present Lake Ontario, the new-born cataract was not the equivalent in height of the escarpment to-day. The Iroquois waters then bathed all the lower portion of the escarpment, so that the foot of the Fall was upon the borders of the Lake.

In order to interpret the history of the Niagara gorge, we must remember that the effective drilling of this gorge was in each stage dependent mainly upon the volume of water discharged from Lake Erie, a large discharge being recorded by a channel drilled both wide and deep, while that produced by the discharge of a smaller volume was correspondingly narrow and shallow. To-day the gorges of large cross section have, moreover, a relatively placid surface, whereas through the constricted sections the water of the river is unable to pass without first raising its level at the upper end and under the head thus produced rushing through under an increased velocity. The best illustration of such a constricted section is the Gorge of the Whirlpool Rapids.

Our reading of the history should begin at the site of the present cataract, since the records of later events are so much the more complete and legible, and it should ever be our plan to proceed from the clearly written pages to those half effaced and illegible.

As we have learned, the most abrupt change in the cross section of the gorge is found a little above the railroad bridges, where the Upper Great Gorge is joined to the Gorge of the Whirlpool Rapids (Fig. 389). In view of the remarkably uniform cross section of the Upper Great Gorge, there is no reason to doubt that it has been drilled throughout under essentially the same volume of water, and that its lower limit marks the position of the former cataract when the waters from the upper lakes were transferred from the “North Bay Outlet” into the present or “Port Huron Outlet” and Lake Erie. As the upper limit of the Gorge of the Whirlpool Rapids thus corresponds to the closing of the “North Bay Outlet” and the extinction of the Nipissing Great Lakes, so its lower limit doubtless corresponds to the opening of that outlet and the termination of the preceding Algonquin stage; for in the stage of the Nipissing lakes the water of the upper lakes, as we have learned, reached the ocean through the northern outlet.

Mr. Frank Taylor, who has given much study to the problem of Niagaran history, believes that the Middle Great Gorge, comprising the Eddy Basin and the Cove section, represents the gorge drilling which occurred during the later stage of Lake Algonquin after the “Trent Outlet” had been closed and the waters of the upper lakes had been turned into the Erie Basin.

Summarizing, then, the episodes of the lake and the gorge history are to be correlated as follows:—

Glacial Lake	Niagara Gorge
Early Lakes Iroquois and Algonquin.	Drilling of the gorge from the Lewiston Escarpment to the Cove section above the Wintergreen Flats.
Later Lakes Iroquois and Algonquin with upper lakes discharging into Erie basin.	Drilling of Middle Great Gorge.
Nipissing Great Lakes with the upper lake waters diverted from Lake Erie.	Drilling of the narrow Gorge of the Whirlpool Rapids.
Recent St. Lawrence drainage since the waters of the upper lakes were discharged into Lake Erie through occupation of the Port Huron Outlet.	Drilling of Upper Great Gorge to the present cataract.

Time measures of the Niagara clock.—In primitive civilizations time has sometimes been measured by the lapse necessary to accomplish a certain task, such, for example, as walking the distance between two points; and the natural clock of Niagara has been of this type. But men possess differences in strength and speed, and the same man is at some times more vigorous than at others, and so does not work at a uniform rate. The cataract of Niagara, charged with the pent-up energy of the waters of all the Great Lakes, can rush its work as it is clearly unable to do at times when the greater part of this energy has been diverted. Units of distance measured along the gorge are therefore too unreliable for our use, with the unique exception of the stretch from the railroad bridges to the site of the present cataract, within which stretch the gorge cross sections are so nearly uniform as to indicate an approximation to continued application of uniform energy. This energy we may actually measure in the existing cataract, and so fix upon a unit of time that can be translated into years.

In order to secure the normal rate of recession of this Upper Great Gorge, we should add to the volume of water in the Canadian Fall that now passing over the American; and for the reason that the blocks which fall from the cataract cornice and are the tools of the drilling instrument approximate to a definite size fixed by their joint planes, the effect of this added energy it is not easy to estimate. We may be sure, however, that the drilling action would be somewhat increased by the junction of the two Falls, and thus are assured that the average rate of recession within the Upper Great Gorge has been somewhat in excess of the five feet per year determined by Gilbert for the present Canadian Fall. The Upper Great Gorge is about two miles in length, and its beginning may thus be dated near the dawning of the Christian Era. The Whirlpool Gorge was cut when the ice vacated the North Bay Outlet in Canada, and still lay as a broad mantle over all northeastern Canada. For the earlier gorge and lake stages, the time estimates are hardly more than guesses, and we need not now concern ourselves with them.

The horologe of late glacial time in Scandinavia.—A glacial timepiece of somewhat different construction and of greater refinement has been made use of in Scandinavia to derive the “geochronology of the last 12,000 years.” Instead of retreating over the land and impounding the drainage as it did so, the latest continental glacier of Scandinavia ended below sea level, and as it retired, its great subglacial river laid down a giant esker known as the Stockholm Os, which was bordered by a delta and fringed on either side by water-laid moraines of the block type. These recessional moraines are upon the average less than 1000 feet apart, and are believed to have each been formed in a single season. The delta deposits which surround the esker are of thin-banded clay, and as an additional uppermost band is found outside every moraine, these bands are also believed to represent each the delta deposit of a single year. In studies extending over many years, Baron de Geer, with the aid of a large body of student helpers, has succeeded in completing a count of moraines and clay layers, and so in determining the time to be 12,000 years since the ice front of the latest continental glacier lay across southern Sweden. The fertility of conception and the thoroughness of execution of this epoch-making investigation recommend its conclusion to the scientific reader.

Reading References for Chapter XXV

G. K. Gilbert. Niagara Falls and their History, Nat. Geogr. Soc. Mon., vol. 1, No. 7, 1895, pp. 203-236.

F. B. Taylor. Origin of the Gorge of the Whirlpool Rapids at Niagara, Bull. Geol. Soc. Am., vol. 9, 1898, pp. 59-84.

A. W. Grabau. Guide to the Geology and Paleontology of Niagara Falls and Vicinity, Bull. N. Y. State Mus., vol. 9, No. 45, 1901, pp. 1-85, pls. 1-11.

J. W. Spencer. The Falls of Niagara, etc. Dept. of Mines, Geol. Surv. Branch, Canada, 1907, pp. 490, pls. 43.

G. K. Gilbert. Rate of Recession of Niagara Falls, etc. Bull. 306, U. S. Geol. Surv., 1907, pp. 31, pls. 11.

G. de Geer. Quaternary Sea Bottoms of Western Sweden. Paper 23, Livret Guide Cong. GÉol. Intern., 1910, pp. 57, pls. 3.

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