The charm which wins and rivets our attention in such pursuits as those of Geology or Mineralogy, is not that the phenomena which we meet with are capable of being classified, and of forming a scientific system. All this is, no doubt, one day instructive and interesting; but it was an afterthought, the result of experiment. The first charm lay in that silent mystery which broods over every part of creation, a veil as yet unpenetrated by Science: it lay in our instinctive consciousness that Nature, in what are, perhaps, her simplest movements, still transcends all the master-pieces of Art.

Take, for instance, the crystalline gems. These are the most remarkable substances with which we are acquainted; they are also among the most simple. Chemically speaking, the metals and gases may claim to be regarded as simpler bodies; but then it must be remembered that we do not meet with them in nature thus unmixed. Gases vary, both in volume and character, every instant; and ordinary metallic ores are penetrated and disguised by foreign matter; whereas faultless crystals, once perfected, appear to be unalterable.

Some of these, as the DIAMOND, would almost seem to be an elementary substance; and yet this can hardly be the actual case. The philosophical account of a crystal, as “some substance, all the particles of which, being free to move, have been operated upon in the way of a chemical, perhaps an electrical change,” certainly makes against it; for, according to this definition, such “substance” is a first desideratum, without which we cannot have the “crystal.” Thus, oxygen and hydrogen, blended together in certain definite proportions, yield the fluid substance, WATER; and the “crystal” of water is ICE. In like manner, common white carbonate of lime, and the fluor spars, whose ingredients we know, are in daily process of formation.

The philosophical idea, so accurately expressed in the above definition, is, doubtless, correct, if once we assume a past history for some substance, and take the crystal before us as its result. But, whether all bodies which we now meet with under the form of crystals have, in point of fact, had such a history, is quite another question.

The diamond is universally held to be pure CARBON crystallized. Its high refraction indicated this to Newton long ago; and the proof has since been given twofold: for the diamond scales off and evaporates under intense heat, and its dust has carbonized iron-filings, turning them into steel.

Further, this carbon is supposed to be of vegetable origin; and, if so, it would seem to follow that there must have been plants, and perhaps coal-strata, before there could be any diamonds.

But what was the process actually carried out in nature? No one has hitherto succeeded in obtaining this gem, answering to the conditions of a “brilliant” in water, lustre, and weight, by any attempted method, from the base of carbon. The French chemists have now, for some years past, been experimenting upon boron, by means of the voltaic battery; and they have, it seems, taken out of the crucible sundry small, pale crystals, which are found to be nearly as hard as adamantine spar (a variety of corundum); but they cannot show, as the fruit of their labours, a diamond weighing one carat, and worth, according to the tariff, eight pounds sterling in the market of Europe. Indeed, if this boron be a mineral intermediate between carbon and silex, their gems will assuredly partake of the character of rock-crystal, a stone which has no affinity with the diamond whatever.

The process of Nature, therefore, being unknown, if indeed it ever took place, the question fairly arises—whether diamond be a derived crystal, or itself an original type of created matter. Or it might be put thus: “If diamond be the purest form of carbon known, what is carbon then but diamond debased?”

Neither does this exhaust the argument. The ruby owns a matrix: the pearl grows in the mother-of-pearl. What is the nature of the diamond-rock? Is it a dark conglomerate? or is it diaphanous?

We know how diamonds are obtained: how they are picked out of the crevices of certain rocks, and washed out of the sands of certain rivers—in the Carnatic, and Brazil, and Borneo; but we do not seem to be much nearer to the history of their parentage.

Again, what is their “crust” or coating with which they are always found enveloped? Is it an integral part of the stone, or is it adventitious? In the best diamonds this crust is of a greenish hue.

Some say that while the gem itself has positive electricity, its crust shows negative. If this be so, the last question is answered—the crust in that case cannot be an integral part of the stone. The only absolute reason I know of for concluding the diamond to be a derived substance is, that it is laminar. The Eastern lapidaries, as it is well known, will sometimes divide a stone by striking it a sharp blow in the cleavage.

After all, the most extraordinary property of the diamond, as pure carbon, is its weight. It is fifty times the weight of refined charcoal. How was the element of carbon condensed and inspissated thus? Was it by the action of LIGHT? This is the vegetable analogy; as we see in the case of all growing plants: did it hold here?

If we were to inquire how oriental sapphires, including the ruby, the blue sapphire, the emerald, and the amethyst, are formed from CLAY, that clay which exists in the granite rocks, the difficulty would be nearly as great. We do not know at all.

But there is some satisfaction in having undoubted proof of the nature of their “base.” And the obvious evidence upon this point is very simple, and prior to that of chemical analysis. My own attention was first drawn to it many years ago, in a casual remark made by a friend. We were handling some crystals of the white sapphire, a stone of little value. “These look very like glass,” said I. “Yes, but you may always tell them from glass by their coldness. Touch one with your tongue.” Then followed the inquiry. “And why is it so much colder than glass is?” “Because the ‘base’ of the sapphire is CLAY, and clay is a very cold substance.”

Let us now pass on to consider the question of COLOUR. In the existing varieties of gems, we have all the colours of the spectrum perpetuated and vivid.

What is the source of these colours? And how are they blended with the solid crystal?

There seems to be no reason for doubting that the immediate source or cause of colour is the presence of some oxidized metal. All the colours which Nature has impressed appear, as far as we can trace them, to be due to such a presence. Opaline tints, and those of the “cat’s eye,” are an exception; being the perceptible result of a peculiar texture and configuration; so also are the iridescent hues on a soap-bubble, which are probably caused by polarized light. But it is a metal which makes the bark of certain trees and shrubs to glisten; aided, in the case of the birch and wheat-stubble, by particles of silex. It is a metal, absorbed from juices of the soil, which gives their tints to flowers, and their deep tinge to fruits. It is a metal which dyes the plumes of the king-fisher; and the gleaming scales of the dragon-fly and diamond-beetle owe their brilliancy to metallic lustre. Why should this all-pervading law vary in the crystals?

We know that metals proper affect crystalline forms, assuming them spontaneously; and we know that the gems have come in contact with metals. Iron, whose rust is of a reddish hue, enters into many of them; and in the red stones it is said to be abundant.

Probably, the finer permanent tints are due to gold, in infinitesimal proportions. Professor Faraday has said that the ruby-tinted glass called “Bohemian” derives its colour from gold in a pure form, finely attenuated, and not from any chemical combination of that substance.

A white diamond has far more lustre than one which is yellow or violet-tinted. But in all the sapphires, the deeper the hue, the more brilliant and valuable the stone. Hence the technical term for the colour of a diamond is its water. In all these gems the hues (whatever their origin) are homogeneously united with the crystal; and the modus operandi of Nature is a profound secret.

When we descend in the mineralogical scale, and come to such stones as agates and jaspers, the process which has been followed seems quite capable of being traced—for its antiquity is not so great. The colours which we now find in pebbles more or less opaque, though occasionally lively, exist under very different conditions from those by which they reside in the crystalline gems. It is necessary, however, to consider first, the origin and nature of pebbles as distinguished from casual fragments of stone.

This was long held to be one of Nature’s riddles; but as soon as it was experimentally dealt with, it met with a solution in some of its most difficult points.

It was early decided that pebbles are distinct formations, complete in themselves, except in so far as they have been worn away by gradual attrition. The first difficulty was, how to account for the great hardness of many of our seaside specimens. Although for the most part inclosing an “organism,” which must have been that of some zoophyte, they show no traces, in their present compact texture, of the soft and yielding consistency they must at that time have possessed. The matrix in which they lie, and from which they drop as the ripe nuts fall from a hazel-bush, is seldom or never of so hard a substance as are the pebbles themselves; in many cases the difference is as great as between the teeth and gums of a living mammal.

But the evidence of the inclosed organism is conclusive as to a past history; and in all mixed pebbles—and ninety-nine out of a hundred of ours are mixed—it is quite certain that an impregnation, or an actual infiltration, has taken place.

Either a fluid menstruum, usually siliceous, must have enveloped and saturated the animal form, or there was actual injection of chalcedony and limestone, in a soft state, into the tubes and cells of the skeleton first, and afterwards into the pores and crevices of the new stone. Frequently both processes have obtained. The only alternative, viz. that which suggests that composite pebbles, revealing in their structure distinct traces of animal or vegetable organization, may have been formed thus at first, like the coloured prints in a book, I consider to be untenable. One might as readily credit a spontaneous growth of almond-cakes or oyster-patties by some sudden spasmodic effort of our present sea and land.

Impregnation has, no doubt, been always going on.

A French savant, M. Reaumur, above a century ago, wrote as follows:—“By a coarse operation emery is reduced to powder and suspended in water for several days; but nature may go much further than this, for the particles which water detaches from hard stones, by simple attrition, are of an almost inconceivable degree of fineness. Water thus impregnated contributes to the formation of pebbles by petrifying the stone, as it were, a second time. Stones already formed, but having as yet a spongy texture, acquire a flinty hardness by impregnation with this crystalline fluid.”[3]

From such a source, as he supposes, has arisen the close texture of Egyptian pebbles, coloured jaspers, and even agates. If he means to include the homogeneous agates, which are alike free from sparry crystals, metallic scum, and all traces of organized matter, I do not agree with him. But in the case of mixed chalcedonic pebbles, among which may be classed our pretty Isle of Wight specimens, no doubt such impregnation took place, and was followed by a further process of infiltration. For when the flint-nodules, impregnated as above, were still soft—soft enough we know they were to take delicate impressions of the spines of the echinus—chalcedony, in a semi-fluid or viscous state, would pass through the pores of the flint, because the former is the finer substance of the two. And after such infiltration, the entire lump would harden, resisting, for the most part, further change. And this would be the pebble as we now find it.

In the “Geological Museum,” now open in Jermyn Street, there is a case (on the first floor) where the nature of infiltration is well shown in some jasper-agates. It will readily be seen here that each internal layer has been formed in succession from without, the centre of the pebble filling up last. In another case (labelled “Silica”), on the opposite side of this room, are some “choanites” and “sponges” presented by the author.

Those latter will be found worthy of ten minutes’ inspection, even as seen through the plate of glass which serves to protect them. They are selected, not as being the finest specimens in his cabinet, but as illustrating, each of them, a particular animal, or a peculiar position of one in the fossil state. They are, however, very good specimens, much above the average; and if any one became missing, it could never be exactly replaced, though you should search the world over. Nature does not stamp the same “medal” twice. Any person who, after examining these, likes to start a theory of his own to account for their forms and colours, has my full permission to do so. But one word I would say in friendly warning, seeing that theories do abound. The Chinese, that ancient and wise people, have a theory that “asbestos” cloth may have been manufactured “of the hair of certain rats that lived in the flames of certain volcanoes.” It were monstrous to doubt it.

In my beach-rambles I have often picked up and examined globes of sandstone which were partially chalcedonized, and that by evident infiltration. The lapidaries call these “sand-agates,” and reject them as unfit for the wheel; and so they are at present, but it would be instructive to meet with some of them twenty years hence, after they had undergone a more confirmed treatment at the hands of Dame Nature.

The well-known specimens of “petrified wood,” common on our coasts, and occurring in some beautiful varieties of beech and acacia in the bays of South Devon, are a further example of infiltration; but the process here must have been somewhat different.

The presence of metallic particles, what lapidaries term the “moss,” in many of our agates, argues an impregnating fluid, thoroughly charged with mineral matter. In most cases this fluid was a ferruginous stream, such as may often be seen issuing from some hidden reservoir, and trickling down the face of a cliff of gault or greensand. This tinges everything that lies in its path with an indelible red stain; it then oozes on through the shingle, and reaches the verge of the sand. The nearest pool becomes saturated between tides, and the suspended crystals of salt, which are of a penetrating character (as the state of your beaching-boots will soon inform you), enter into chemical combination with the metallic rust, and help to conduct its particles into the heart of many a limestone pebble.

Dark inland pebbles, on the other hand, will discharge much of the oxide which they have imbibed, and may be observed to brighten and improve their complexions after a few months’ sponging and tossing in the purer sea-water.

Some of our handsomer pebbles, when cut in two, reveal blotches of metal, which are glossy after polishing on the wheel. This metal is occasionally native iron. The darker varieties of “moss” contain a good deal of manganese, and some silver.

From what has been said about impregnation, we may readily conclude that the colours found in our agate-pebbles have been chemically inwrought, and that the symmetrical patterns, over which these colours are disposed, are not due to a succession of “layers,” as in the ribbon-jaspers and Scotch pebbles, but must be referred to the organization of some extinct zoophyte, whose skeleton is preserved in the existing fossil.

The cause of translucency, or even transparency, in some pebbles is, no doubt, to be sought in their finer and more even texture, but especially in the latter quality. Sir Isaac Newton was of opinion that the opacity of certain substances is simply a result of their cross-grained composition. He held that in a transparent body the particles must be regularly and evenly disposed at equal intervals, so that a ray of light entering such a substance would pass steadily on, according to the known laws of gravity and motion, meeting with no obstruction beyond that of the homogeneous density of the medium which it had to traverse. Whereas, in opaque bodies, he supposes these constituent particles to be unevenly disposed, and that the ray which enters at the surface is, as it were, pushed about and thrust aside, and at length lost to sight.

The purity of spring-water, when undisturbed, illustrates this beautiful theory of the great philosopher; and, among solid substances, good glass, especially plate-glass which, after fusing in the furnace, has been carefully run and settled in the frames. It may also be simply shown in the act of wetting or steeping certain dry substances. Thus, stout writing-paper, owing to its cross texture, is opaque when dry; but if we immerse a sheet of it in oil, and then hold it up to the light, we find it has become transparent. For the smooth medium thus imbibed has entered its pores, and equalized the general texture.

We find also a striking argument for the probable truth of Newton’s eagle-eyed conclusion in certain minerals which possess double refraction.

ICELAND SPAR, one of these, is perhaps the most perfectly transparent solid with which we are acquainted. Now, Iceland Spar transmits both the rays, as we see in the twofold image which is presented to us. But TOURMALINE is opaque, even the red specimens looking almost black; and we find that Tourmaline absorbs one of the two rays of polarized light. This singular stone polarizes a beam of light if it enter in any direction but that of the longer axis.

No solid with which we are acquainted is absolutely transparent. And there is no perfect reflector known. The best-polished surface absorbs nearly one-half of that quantity of light which strikes upon it.

As to our seaside pebbles, the most compact of them are even visibly porous. Cut through the hardest jasper, and polish one face till it shines like a steel mirror, and then hold it so as to reflect the light, you will at once discern numerous minute specks or flaws on this surface, as if the point of a needle or graving-tool had been busily at work upon it. These specks have always been there. They are air-holes, and in the case of a fossil-pebble were, some of them, doubtless, connected with the position which the animal occupied just before he died. These air-holes must have traversed this hard stone in every direction, for, cut the pebble how you will, you meet with them. Others again, incomparably more numerous, but which can scarcely be discerned without the aid of a powerful microscope, are the true pores belonging to this apparently impenetrable substance.

I have found that the action of daylight tells even upon polished agates after a time. Some of the spots and markings in the finest stones grow fainter in the course of many years. Others appear to deepen. This is, no doubt, a change resulting from the oxygen, contained in a beam of light, acting readily upon carbon, silex, and other substances. And it furnishes an independent argument for concluding that the visible beauty of these formations, in perpetuating a coloured pattern, has been due rather to mixed chemical processes than to pure crystallography.

The fossil nodules, mostly siliceous, which we find upon a sea-beach, are integral specimens. It never but once happened to me to meet with what appeared to be two choanites in the same pebble, and I incline now to believe that this was in fact one choanite who had divided himself after the manner of the Luidia. But even supposing that here were, indeed, a pair of perfect animals, when it is considered that this was one single instance, occurring among more than a thousand picked up by me, in which the choanites were always solitary, such an exception may be almost said to prove the rule.

The late lamented Hugh Miller has stated the like fact concerning his Morayshire and Cromarty icthyolites. At pp. 194, 195, of his “Cruise of the Betsy,” he remarks that “the limestone nodules take very generally the form of the fish which they inclose; they are stone coffins carefully moulded to express the outline of the corpses lying within.” Then, after observing that the shape of the stone conforms to the attitude of the fish in every instance, he goes on to state that “the size of the fish regulates that of the nodule. The coffin is generally as good a fit in size as in form; and the bulk of the nodule bears almost always a definite proportion to the amount of animal round which it had formed.”

He then gives, in his usual clear and graphic language, the following remarkable statement, the result of direct experiment.

“When a calcareous earth, mixed up with sand, clay, and other extraneous matters, was deposited on some of the commoner molluscs of our shores, it was universally found that the mass, incoherent everywhere else, had acquired a solidity wherever it had been penetrated by the animal matter of the molluscs. Each animal, in proportion to its size, was found to retain, as in the fossiliferous spindles of the Old Red Sandstone, its coherent nodule around it. Here the animal matter gave solidity to the lime in contact with it. But in the natural phenomenon of the icthyolite beds, there was yet a further point, for in these the animal matter must have possessed such an affinity for the mineral, as to form, in an argillaceous compound, a centre of attraction powerful enough to draw together the lime diffused throughout the mass.”

Hugh Miller concludes the above passage by saying that “it still remains for the geologic chemist to discover on what principle masses of animal matter should form the attracting nuclei of limestone nodules.”

Upon which last remark, I would suggest that the principle of the “law of definite proportions,” established by Dalton, and fully borne out by all succeeding experiments in chemistry, appears to meet the case, geologically as well as chemically, in every respect. For such a law must of course obtain, whether the chemical ingredients be present in the forms of mineral, vegetable, or animal life; in fact, we have never known the law to vary. It holds for the compounded elements which we term AIR and WATER; it holds for the crystals; it holds for vascular and cellular tissues; why should it fail when the further instance of a mollusc or a zoophyte is in question?

I see no reason to doubt that the blood, muscle, membrane, or adipose matter of any animal have their due respective affinities for the different substances of the mineral creation.

No doubt, however, electricity, as an active cause, bears directly upon all such phenomena.

I remember many years since being greatly perplexed with the discovery (as I then thought it) that in certain parts of the Isle of Wight, and along the Dorsetshire coast, the rows of dark flints imbedded in the upper chalk of the cliff-ranges were all broken; broken small, so that if one were taken out of its chalk socket it crumbled in your hand. Often and often, I turned this fact over in my mind, and sought some apparent way to account for it. But I think I now see one way to account for it; and which may perhaps be judged worthy of acceptance, until a better solution is hit upon. In Dr. Hook’s experiment with that once common household implement, the “flint and steel,” he found that the sparks which “fly” upon collision taking place are minute spherules of metal. And further, that this metal was now not steel any longer, but iron; the fragments struck off having lost their polarity in the moment of contact with the flint.

This experiment shows that silex possesses some remarkable affinity for the magnetic fluid, since in this case it had robbed the steel of it, for those spherules would not answer to the magnet. May not, therefore, the rows of flints in the cliff have attracted the lightning in severe thunderstorms, and been shivered by the blow? This would not necessarily hurl the chalk down.

The Arabs have a proverb which says, “Under the lamp it is dark.” Certainly, the chief mystery of every animated creature seems to reside in its life, and Life is like a burning lamp. Once the life extinct, we can anatomize and analyze, and arrive at many partial conclusions; but, meanwhile, the life has departed, and we do not know what that was. The nearest thing to its likeness is expression; and animals rank high in the scale of being, according as they command and impart expression. A dog or horse have a great deal; a bird some; a reptile or insect, absolutely none to our eyes.

With these latter, however, their habits, while alive, take the place of any more intelligent expression; especially some of their more excited movements. We know by the sound, when a snake is angry; and as to motion, the attack of a provoked hornet is a startling thing to witness. Ordinarily speaking, however, all their habits tend to concealment; no doubt, for the sake of safety. I believe no one ever sees the Sphynx-moth, called a “Death’s-head” (Acherontia Atropos), on the wing. Yet we discern many others which, like it, fly in the hours of dusk. But this insect whirls through the air like a stone from a sling. It has never yet, in my experience as a naturalist, been my lot to meet with the burrowing insect called an Ant-lion. Only twice in my life have I encountered a slow-worm in the woods of Devon and the Isle of Wight. And to instance the case of a far commoner creature, how seldom does it happen to any one to take the large dragon-fly behind his green leaf!

And yet the problems of inanimate matter are perhaps the most difficult to solve. They have deeply exercised philosophers in every age of the world.

“All things considered,” says Newton, “I think it probable that God, in the beginning, formed matter in solid, hard, impenetrable, movable particles; of such sizes and figures, and with such other properties as most conduced to the end for which He formed them. And that these primitive particles, being solids, are incomparably harder than any of the sensible porous bodies compounded of them; even so hard as never to wear, or break in pieces; no other power being able to divide what God made one in the first Creation. While these corpuscles remain entire, they may compose bodies of one and the same matter and texture in all ages; but should they wear away or break in pieces, the nature of things depending on them would be changed. Water and earth composed of old worn particles and fragments of particles, would not be of the same nature and texture now with water and earth composed of entire particles at the beginning. And therefore, that Nature may be lasting, the changes of corporeal things are to be placed only in the various separations and new associations of these permanent corpuscles.”

So wrote the man, “Qui genus humanum ingenio superavit,” who at the age of twenty-four had already invented the Fluxional Calculus, discovered the Decomposition of Light, and enunciated and proved, in a series of lemmas, the law of Universal Gravitation.

But soft! What is this which steals upon our senses through bobbing apple-blossoms at the open casement? It is the delicious, oystery smell of the Sea, as the afternoon tide runs in with a sound like that of fairy-bells upon the sand and rock and loose shingle.

That scent, and sight, and sound, are altogether irresistible. We throw aside Dr. Buckland and Hugh Miller, clap on a “wide-awake,” rush down at once by the zig-zag path, and madly catch up a bunch of dripping tangle, and kick a hole in the moist sand, and presently find that our “Balmorals” are ancle-deep in the brine of a nimble wave.

And now I descry a faint purplish hue upon the red beach which lies at the foot of Culver. To-morrow, we will breakfast early, and hunt up a score of pebbles before the day grows hot.

[3] “MÉmoires de l’AcadÉmie des Sciences.” Anno, 1721.