Gypsum and Marls.-Gypsum is a crystalline substance composed of lime, in union with sulphuric acid and water. Its colours are grey, white, and yellow; but different varieties of it have different hues. It was used in ancient times for window glass. The gypseous rocks consist of an alternation of gypsum and limey and clayey marls; these marls are also found in thick beds above this alternation. These beds are considered as having been deposited in fresh water, and above them are others, which, from their organic remains, are believed to have been deposited in the sea.

Upper Marine Sands and Sandstones.-These consist of irregular beds of siliceous sandstone and sand. The animal remains in the lower portion of these beds are broken and very rare. In some situations, however, millions of small bodies have been found. These beds are occasionally covered with a species of rock which is filled with marine shells.

Upper Fresh-Water Formation. This rock sometimes consists of white calcareous marls, at others of different siliceous compounds; from one of these, millstones of a celebrated kind are formed. They are sometimes charged with shells and petrified wood.

of such explanations as leave the general truth unshaken.

In the Tertiary Formation we find a striking and wonderful change of appearances. These strata are rich beyond all that go before them in animal remains. At the time of their formation, the aptitude of the earth for the maintenance of organic life had vastly increased, and was continually increasing, as the period approached when man himself and the higher orders of being were to become its inhabitants. The way was paved, it will be seen, for this consummation, by the same regular and progressive steps which characterised the organic changes of the geological eras already described.

From their relative position, and from the organic remains contained in them, geologists have been enabled to distinguish, in the tertiary series of strata, four great eras of formation. One of the most striking and novel features of these formations consists, as already mentioned, in the repeated alternations of fresh-water deposits with marine ones; a circumstance established beyond question by the character of the fossil shells and bones found respectively in these deposits. To The supracretacious rocks of England are commonly the oldest of the tertiary eras, the term Eocene is apknown by the names of plastic clay, London clay, Bag-plied: the second is called the Miocene period; the shot sands, the fresh-water formations of the Isle of third, the Older Pliocene; and the fourth and latest, the Wight, and the crag of Norfolk. Newer Pliocene; names founded on the respective proportions which their fossil shells bear to shells of existing species. In each of these periods is included a great fresh-water, as well as a marine, formation or deposit. Of the living beings which flourished in each of these periods, we shall endeavour to give some account, commencing with the most ancient, the Eocene.

Plastic Clay-This deposit, though it occasionally contains an abundance of clay, employed for various useful purposes, is also mixed with beds of pebble, irregularly alternating with sands and clay. It thus differs from that of Paris, but it agrees with it so far as it reposes upon an uneven surface of chalk. The organic remains are principally marine, but those of freshwater and terrestrial animals are intermingled with them.

London Clay-The great argillaceous deposit which underlies the London district, has obtained this name. It is of a bluish or blackish colour, and contains a portion of calcareous matter; beds of sandstone are also said to be occasionally present in it. This clay varies considerably in thickness, sometimes from seventyseven to seven hundred feet. Besides the remains of a great variety of shell-fish, those of a crocodile and turtle have been found; masses of wood have also occurred in this stratum.

Bagshot Sands. These rest upon the London clay, and consist of layers of various kinds of sands and marls containing fossil shells.

After the chalky formation, a period of considerable repose seems to have ensued, during which a large I portion of the existing continents, and in especial the hollows and basins on their surface, appear to have been the site of vast lakes, rivers, and estuaries. From these was deposited the first great fresh-water formation of the Eocene period. While this deposit was going on, the globe, no longer an entire stagnant marsh, but as yet incapable of affording much support to terrestrial animals, was tenanted only by such quadrupeds as live beside rivers and lakes. Nearly fifty extinct species of mammalia, chiefly of this character, were discovered by Cuvier in the first Eocene fresh-water formation. The most of these belonged to the class Pachydermata (thick-skinned animals), of which the elephant, the rhinoceros, the hog, the tapir, and the horse, are remarkable existing examples. This class of Pachyder matous animals, it may be observed, only includes such thick-skinned creatures as have no more prominent mark to distinguish them than their skins. The seal and river-horse, for example, are thick-skinned, but then they are amphibious, and that is a more prominent distinction. The extinct animals to which we now refer It may be observed, that volcanic agency has been resemble the tapir more than any of the other Pachyvery active during the formation of this group. Etna, dermata. Among these extinct creatures, the most it would appear, has for a long series of ages given forth worthy of notice are the Palæotherium, the Anoplotheits igneous products, and a considerable portion of these rium, the Lophiodon, Anthracotherium, Cherapotamus, rest upon supracretaceous rocks. In central France, and one or two other families, including, some of them, where extinct volcanoes are numerous, this is still more not less than eleven or twelve distinct species. These evident: a volcanic mass, called the Plomb du Cantal, mammiferous families had some general traits of resemappears to have burst through and fractured the fresh-blance, and the description of the great Palæotherium water limestones of the Cantal, which, according to Mr Lyell, are equivalent to the fresh-water deposits of Paris, and some of those in England.

The Isle of Wight and London formations, although differing considerably in the nature of their deposits from those of Paris, present such an analogy in the organic remains of some parts of the group, that we are justified in referring the deposit to the same epoch, local circumstances and accidents having determined their characters.

Fossils of the Tertiary Series.

As yet, no distinct traces of the higher forms of organisation have appeared. No vestiges of the mammiferous or sucking animals, either terrestrial or aquatic, which form so large a portion of the existing animal kingdom-no marks of the bird class, now so extensive and important-and scarcely any token of such marine and fresh-water shells and other productions as abound in the present time-have been discovered either in the earlier or later secondary strata of the globe. The rare, and indeed almost unique, cases of supposed exception to this statement, have all been found capable

may afford an idea of the main features of all. This animal was of the size of the horse, or about four feet and a half in height to the wither. It was more squat and clumsy in its proportions than the horse; the head was more massive, and the extremities thicker and shorter. On each foot were three large toes, rounded, and unprovided with claws; the upper jaw was much longer than the under. The tapir, and partly, also, the hog, if large enough, would closely resemble the great Palæotherium. The Palotheria (says Buckland) probably lived and died upon the margins of the then existing lakes and rivers, and their dead carcases may have been drifted to the bottom in seasons of flood." The other mammiferous families of the first Eocene formation, were all, like the Palæotheria, herbivorous, and had, it is probable, similar habits.

The number of animals, aquatic and terrestrial, whose remains are found in the other deposits of the Eocene period, is immense. In some gypsum (sulphate of lime) quarries of that era, scarcely a block can be opened which does not disclose some fragment of a fossil skeleton. The following list of the animals found in the gypsum quarries of Paris, will show sufficiently how very different from the gigantic reptiles of the secondary eras were the creatures that tenanted, and found fitting sustenance on, the earth during the Eocene period. Besides various extinct Pachydermatous families, there were found extinct species of the wolf and fox, of the racoon and genette, among the Carnivorous tribes; of the opossum; of the dormouse and squirrel; nine or ten species of birds, of the buzzard, owl, quail, woodcock, sea-lark, curlew, and pelican families; fresh-water tortoises, crocodiles, and other creatures of the Reptile class; and several species of Fishes:-all of these animals, be it remembered, being extinct species of existing | families, exclusive of the Pachydermatous animals, and the Fishes, which were extinct species of extinct families. The occurrence of the birds mentioned in the preceding list of the Eocene animals, forms (says Dr Buckland) "a remarkable phenomenon in the history of organic remains." The number of fossil shells found in the Eocene formations is estimated by Mr Lyell at 1238. As in the case of the terrestrial creatures, few of these shell-fish are of recent or existing species, not more, at the utmost, than 34 in every hundred. We do not, moreover, recognise in the strata now under consideration, those prodigious accumulations of microscopic shells, as they are called from their extreme minuteness, that distinguish the formations of the secondary or preceding ages. One small piece of rock, of the ages in question, has been found to contain above ten thousand chambered shells, though the whole weighed only an ounce and a half. In fact, great beds of secondary limestone seem to be almost wholly composed of microscopie shells. Such phenomena are not presented in the Eocene or subsequent tertiary formations. The shells of these periods, as has been already observed, approximate more to the character of recent or existing species.

tioned two skeletons of the Dinotherium, a large herbi vorous animal, called by Cuvier the Gigantic Tapir; two large Tapirs; Calicotherium-two large Tapir-like animals of this name ; two Rhinoceroses; Hippotherium, an animal allied to the horse; three Hogs; four large Cats, some as large as a lion; the creature called the Glutton; Agnotherium, allied to the dog; and Machairodus, an animal allied to the bear. From this list the reader will perceive the gradual approach in the Miocene animals to existing species. The largest of the terrestrial mammalia yet discovered belongs to the period now under notice; it is the Dinotherium, or Gigantic Tapir, already mentioned. No complete skeleton has yet been discovered; but from the bones found, Cuvier and others imagine the animal to have reached the extraordinary length of eighteen feet. The most remarkable peculiarities of its structure consist in two enormous tusks at the end of its lower jaw, and the shoulder-blade, which resembles that of a mole, and is calculated to have given the power of digging, or other free movement, to the fore-foot. It seems probable that this stupendous creature lived in fresh-water lakes, and had the half terrestrial half aquatic habits of the walrus or river-horse. The tusks might be used in digging up roots and plants, and also in sustaining the head on banks during sleep, or in pulling the body out of the water, as the walrus uses a similar pair of tusks. "In these characters (says Buckland) of this gigantic, herbivorous, aquatic quadruped, we recognise adaptations to the lacustrine (lake-covered) condition of the earth, during that portion of the tertiary periods, to which the existence of these seemingly anomalous creatures seems to have been limited."

In the Miocene period, the seas became the habitation of numbers of marine mammalia, consisting of Dolphins, Whales, Seals, Walrus, and the Lamantin, or Manati. Few of these animals were of the same species as those which exist at present, but the differences were far from being great or remarkable. This circumstance, as well as the considerable number of fossil shells identical with existing ones, exhibits an approach in the character and tenantry of the Miocene seas to the present state of things in these respects. The discovery, also, of true terrestrial mammalia, as the Rhinoceros and Hog, in the Miocene formations, shows, that since the era of the gigantic reptiles, no slight portion of the earth's surface had assumed the condition of dry land, fit for the support of the common herbivorous creatures. At the same time, the occurrence of such animals as the Dinotherium in the Miocene strata, proves, as Dr Buckland remarks, that many regions were still covered with great lakes and estuaries.

It now remains to inquire into the nature and peculiarities of the animals characterising the Pliocene age, which, for convenience, has been arranged into two periods, the Older and Newer Pliocene, the latter of which immediately preceded the formation of the Diluvial layer constituting the present superficial matter of the globe.

In the Eocene period, then the earliest of the Tertiary eras-we perceive, for the first time, the existence in the animal kingdom of a similar order to that which now prevails, indicating that the earth and its atmosphere were in a certain degree assimilated to their present condition. It seems impossible, however, to agree with Mr Lyell in the subjoined remark on the Eocene era:-" When we reflect (says that writer) on the tranquil state of the earth, implied by some of the lake-formed and sea-formed deposits of this age, and consider the fulness of all the different classes of the animal kingdom, as deduced from the study of the fossil remains, we are naturally led to conclude that the earth was at that period in a perfectly settled state, and already fitted for the habitation of man." Several strong arguments might be adduced against this conclusion, but we shall only refer to one objection-the Proceeding from the deepest seated portions of the temperature. From the frequency of the remains of terrestrial crust upwards, we find a progressive apcrocodiles and other tropical reptiles in the Eocene proach, as has already been stated, in the character of formations, and from the frequency of palm-leaves and the animal remains to the existing varieties of animal trunks, as well as from other evidences, the atmosphere life. A remarkable proof of this is presented by the may be regarded as having been still at too high a tem- shells of the Pliocene periods. Whereas only eighteen perature for human comfort. Volcanic action, more- in the hundred of the Miocene shells were of recent over, appears to have been of very common occurrence. species, in the Older Pliocene from thirty-five to fifty, The second, or Miocene period, however, of the and in the Newer Pliocene not less than from ninety Tertiary ages, brings us a step nearer to the existing to ninety-five in the hundred, are identical with shells condition of things. A strong proof of this is derived of existing species. This great change is accompanied from the shells alone of the strata of this period. by the disappearance of the Paleotherian family and Whereas only three in the hundred Eocene fossils were others, which formed the most striking animal remains of recent species, of the Miocene shells we find eighteen of the periods immediately preceding. In place of these in the hundred to have existing representatives. Along extinct species of extinct Pachydermatous or thickwith the mammalia, also, of the Eocene period, we find skinned families, we observe in the strata of the Pliocene that the Miocene deposits present us with the earliest periods a vast number of remains of existing Pachyderforms of animals existing at the present time. In Dr matous families, such as the elephant, the rhinoceros, Buckland's Bridgewater Treatise, a table is given, exhi- and the hippopotamus, though these remains belong to biting the animals found at Darmstadt, in a bed of sand varieties that are now extinct. The first traces also now referable to the Miocene period. In this list are men-appear of Ruminant animals-of oxen, deer, camels,

and other creatures of the same class. But though it | observed. The Megatherium was discovered towards is of importance to notice the existence of such remains the end of the last century. A skeleton, almost entire, in the Pliocene ages, in order to exhibit the progressive was found nearly at one hundred feet of depth, in excaapproach to the present state of things in the animal vations made on the banks of the river Luxan, several kingdom, it is in the huge and extraordinary creatures, leagues to the south-west of Buenos Ayres. The Menow no longer to be seen on the face of the earth, that gatherium was a tardigrade (slow-moving) animal, like the interest of such an investigation as the present the sloth, and was at least the size of a common ox. chiefly lies. The Pliocene ages are not less rich in Its limbs were terminated by five thick toes, attached these wonders than the periods already described, and to a series of huge, flat, metatarsal bones, or those bones to this portion of the subject we shall now turn our with which the toes are continuous, as in the human attention. foot. "Some of the toes (says Buckland, in his notice of this creature) are terminated by large and powerful claws of great length; the bones supporting these claws are composed partly of an axis, or pointed core, which filled the internal cavity of the horny claw; and partly of a bony sheath, that formed a strong case to receive and support its base." These claws, from their position, were admirably calculated for the purpose of digging. The legs of this creature were of enormous thickness, its thigh bone being nearly three times the thickness of the same bone in the elephant. The other bones of the Megatherium were almost proportionably heavy. A still more remarkable feature, however, in the animal's structure, was the coat of armour, of solid bone, varying from three-fourths of an inch to an inch and a half in thickness, which covered its hide, in the same manner as the armadillo's is encased by the same substance.

The enormous creature called the Great Mastodon, belongs to the Pliocene era. Of all the fossil animals whose skeletons have been found complete, or nearly so, the Mastodon is the largest. Much confusion has existed relative to this animal's true character, many naturalists regarding it as an extinct species of the elephant, and others holding that it approached nearer to the hippopotamus. Cuvier, however, determined it to be the head of a distinct family, comprehending several other species. It is about one hundred and twenty years since remains of the Mastodon were first discovered in America, and vast quantities of them have been since found in the same region, buried chiefly in marshy grounds. One skeleton nearly complete was dug up on the banks of the Hudson in 1801, and it is from this that a correct knowledge of the animal has been principally derived. In height, the Mastodon seems to have been about twelve feet, a stature which the Indian elephant occasionally attains. But the body of the Mastodon was greatly elongated in comparison with the elephant's, and its limbs were thicker. The whole arrangement of the bony structure resembled that of the elephant, excepting in one point, which Cuvier regarded as of sufficient consequence to constitute the Mastodon a different genus. This was the cheek-teeth, which are divided, on their upper surface, into a number of rounded, obtuse prominences, arranged not like the elephant's, but like those of the wild boar and hippopotamus; whence it is concluded, that, like the latter animals, the Mastodon must have lived on tender vegetables, roots, and aquatic plants, and could not have been carnivorous. The lower jaw of the skeleton found on the Hudson is two feet ten inches in length, and weighs sixty-three pounds. Like the ele-tion to an animal, whose occupation of digging roots for phant, the Mastodon had two tusks, curving upwards, and formed of ivory, and, in the opinion of Cuvier, it had also a trunk of the same kind with the former animal's.

Altogether, making an allowance for several additional feet of length, the larger specimens of the elephant must be considered as varying little from the Great Mastodon. Though not an aquatic animal, the Mastodon, as has been mentioned, appears to have lived, like the hippopotamus, on aquatic vegetables, and this is corroborated by the marshy situations in which its remains are generally found in the greatest profusion. The Indians of Canada had observed these bones, and believed them to belong to a peculiar animal which they called the father of oxen. There have been found many bones, belonging, it is conceived from the teeth and other peculiarities, to smaller varieties of the Mastodon. No complete skeletons, however, having been yet dug up, it is unnecessary to attempt any detailed description of what these minor Mastodons must have been. From the immense number of Mastodon bones which have been dug up in various parts of the earth, and particularly in the New World, we must conclude that at no distant period of time the terrestrial surface was extensively peopled by these enormous creatures. How strange would the spectacle have been, could a human being have been set down in the midst of the great marshes of the ancient world, and beheld these animals browsing in hundreds, all like moving mountains of living matter! Another creature, belonging to the later Pliocene ages, if not indeed to the era of the Diluvial formation, has been discovered in America, both north and south. This is the Megatherium, an animal more widely removed in character from any existing creature, than any of the other fossil remains that have been yet

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The habits and peculiarities of this stupendous sloth, for so the Megatherium may be termed, are well described and explained in Dr Buckland's Bridgewater Treatise. After stating that with the head and shoulders of a sloth, it combined, in its legs and feet, an admixture of the characters of the ant-eater and the armadillo, and resembled them still more in being cased in a coat of armour, he continues, “Its haunches were more than five feet wide, and its body twelve feet long and eight feet high; its feet were a yard in length, and terminated by most gigantic claws; its tail was probably clad in armour, and much larger than the tail of any other beast among living or extinct terrestrial mammalia. Thus heavily constructed, and ponderously accoutred, it could neither run, nor leap, nor climb, nor burrow under the ground, and in all its movements must have been necessarily slow; but what need of rapid locomo

food was almost stationary? and what need of speed for flight from foes, to a creature whose giant carcass was encased in an impenetrable cuirass, and who by a single pat of his paw, or lash of his tail, could in an instant have demolished the cougar or the crocodile Securo within the panoply of his bony armour, where was the enemy that would dare encounter this behemoth of the Pampas (the South American region where it existed), or in what more powerful creature can we find the cause that has effected the extirpation of his race!

His entire frame was an apparatus of colossal mechanism, adapted exactly to the work it had to do; strong and ponderous, in proportion as this work was heavy, and calculated to be the vehicle of life and enjoyment to a gigantic race of quadrupeds; which, though they have ceased to be counted among the living inhabitants of our planet, have, in their fossil bones, left behind them imperishable monuments of the consummate skill with which they were constructed.”

Another extinct tardigrade creature, presenting many of the characters of the Megatherium, was discovered in a calcareous cavern in Virginia, and received from President Jefferson, who first described some of its bones, the name of the Megalonyr. Jefferson conceived the claw to be that of an extinct feline animal of vast size (that is to say, an animal of the same description as the tiger, lion, cat, and lynx, all of which are beasts of prey); but the French naturalist declared the possessor of the claw to have been herbivorous, or calculated to live on herbs; and this was triumphantly proved by the discovery of others of its bones. The Megalonyx appears (for a complete skeleton has not yet been found) to have been a little smaller in size than the Megatherium. But the Megalonyx, according to Cuvier, was herbivorous after the manner of the

six true grinders in a continued series. The monkey is supposed to have been about three feet in height. The bone occurred in a stratum of marl, covered by compact limestone. Another jaw-bone of a monkey was discovered with other remains, in August 1839, in a brick-field at Kingston, near Woodbridge, in the county of Suffolk: the particular bed in which it was found has not been stated. The bone indicates a species of the quadrumana not now existing.

SECTION IV.-MINERAL VEINS. Throughout the primary, transition, secondary, and tertiary rocks, but particularly the two first kinds, there occur what are called veins, containing diverse substances, most commonly metals, quartz, and calcareous spar, the last being a hard and shining substance deposited from lime. The form and direction of veins may be best understood from the way in which they mostly seem to have originated, namely, by chinks or cracks formed in all directions throughout the rocks, and which have subsequently been filled with various substances.

These must be considered as very interesting discoveries. The earliest animals and plants are of the simplest kind. Gradually, as we advance through the higher strata, or, in other words, as we proceed through this record of progressive creation, we find animals and plants of higher and higher structure, till at last we come to the superficial strata, where there are remains of kinds approximating to the highest of all the animated tribes, namely, man himself. But, before the above discoveries, there remained one remarkable gap in the series. The quadrumana, or monkeys, who form an order above common mammalia, but below the bimana, or human tribes, were wanting. Now this deficiency is supplied; and it is shown that every one of the present forms of animated existence, excepting the human, existed at the time when the superficial strata were formed. The only zoological event of an important nature subsequent to that period is the creation of man; for we may consider of a lesser import-abundance of the metal, at the place where it passes ance the extinction of many of the specific varieties which flourished in the geological ages, and the creation

of new.

VOLCANIC.

Those filled with metals penetrate downwards so far, that their lower ends are rarely found, and miners have an idea that they reach quite through the earth. Near the surface of the earth, they are generally found poorest in the metal they contain, richer at a certain distance down, and then poor again. They also often change their metal at different depths. In France there are veins which contain iron above, then silver, and next copper. One of the Cornwall mines has zinc above, and copper in great quantity below. These veins also change their width at different depths: thus, the Dalcoath mine in Cornwall varies from forty feet to six inches in width.* What at first appears extremely strange, a vein will sometimes be rich, or contain

through one kind of rock, and poor where it passes through another. Thus, for instance, a copper vein will be productive as long as it is dug through slate, and become poor when it passes into granite. Such a vein, it may also be remarked, is generally found richest in the slate when it approaches the granite.

Till a recent time, two theories as to the formation of metallic veins were predominant-one representing them as the result of a forcing of fused matter from below into the chinks, the other accounting for them by supposing an infiltration of the matter in water from above. These theories, respectively termed Hut

Rock of this kind owes its origin to internal fire, which seems to have sent it up in a state of fusion. It is spread over large parts of the surface of the earth, particularly in France, where there are many extinct volcanoes. The apertures through which it has forced its way from below, and the chinks and rents formed at the time of its eruption in adjacent rocks, are often found filled with it. Large mountains are also com-tonian and Wernerian, are now given up: "many veins posed of volcanic rock. It is remarkable for the fine soil formed out of it.

The chief varieties of volcanic rock are—

Trap, a term from the Swedish, expressive of the appearance of stairs which a hill of this rock often presents-a bare precipice alternating with a grassy platform or terrace. In trap rocks, nodules are often found; that is, little isolated masses of a different consistence from the including matter: the rock is then said to be of amygdaloidal structure, from the Greek word for an almond. This peculiarity is owing to the porousness of the original matter: it contained many small aircells, which, being afterwards filled up with silex, carbonate of lime, zeolite, and other ingredients, became nodules of those substances. In plutonic rocks, no such peculiarity is ever found.

are fissures of mechanical origin, into which metalliferous matter has been sublimed from the effects of high temperature; but others have resulted from an electrochemical separation or segregation of certain mineral and metallic particles from the mass of enveloping rock, while it was in a soft or fluid state, and their determination to particular centres.'"+ Within the last few years, much light has been thrown on the subject by electro-chemical experiments, whereby the workings of nature, in this department of her economy, were imitated on a small scale. Becquerell and Mitcherlich, foreign mineralogists, have succeeded in forming crystals by electricity. Our own countryman, Mr Andrew Crosse, of Somersetshire, has in like manner formed calcareous spar out of water which had percolated through a limestone rock, and which was forming crystals naturally at the place where the experimentalist obtained it. The same gentleman produced quartz crystals, and thus made the formation of what are called precious stones no longer a mystery. The electric apparatus used by Mr Crosse was of small power, but kept long in operation, such being the way in which nature works the same ends.

Basalt, a dark grey rock, of crystallised form, masses of which resemble groups of pillars, the various pillars generally having regular sides and angles, and the whole joined compactly together. The Giants' Causeway, in Ireland, and the Island of Staffa, in the Hebrides, are notable examples of basalt. The structure of basalt is found to have originated in the manner in In Mr Crosse's experiments, the same solution prowhich refrigeration, or cooling, took place at its forma-duced different substances at different ends of the tion. The process has been imitated on a small scale by the fusing of a few hundred-weights of basalt, and allowing the mass to cool in the furnace: as the cooling gradually proceeded, globules appeared; these enlarged till they pressed laterally [sideways] against each other, and became converted into polygonal [many-cornered] prisms. Thus the rock was replaced in something like its original form, in a common furnace.

Greenstone, a compact, hard, tenacious rock, of dark greyish colour, slightly tinged with green.

Lava (a term from the Gothic, signifying to run), the product of modern volcanic mountains.

* Lyell's Geology, iv. 272.

electric pole. For example, a battery operating for six
months on fluat of silver, produced at the negative polo
six-sided cubes of silver, and at the positive crystals of
silica and chalcedony. This opens up a most interest-
ing field of speculation. The difference of substances
found in certain veins, their comparative richness and
poorness, may have been the consequence of different
electric states in the rocks in which they were deposited.
* Comstock's Geology, New York, 1836.
Mantell's Wonders of Geology, 651.

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