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sunk; valleys have been excavated, filled up, and again dug out; sea became dry land, and land became sea; yet throughout all revolutions, and the accompanying vicissitudes of climate, animal and vegetable life was sustained, a continual modification fitting it for the different ages and stages of the world. A close analogy is shown to exist between extinct and recent species, and the continuance of the same organic laws is thus evidenced: ancient lakes in the Upper Miocene had round their borders belts of poplars and willows and shrubs. Leaves resembling those of the tamarind, with a ripe seed-vessel, have been found, and, on the same slab, a winged ant. We learn from this that the seed was ripened in summer, at which season alone ants have their wings fully developed, and make their flight.

In venturing upon a short sketch of chemical geology, or of what may be termed the cosmogenetic era in the history of our globe; and then explaining some of the phenomena of the great changes from that early period down to the present time; principles, rather than details of chemical action, will be dealt with.

Exact knowledge shows that mere fire and water are not the only great agents; the geologist must take into consideration the effects which are wrought by chemical action, heat, light, electricity, and mechanical force. It is known that mechanical force may be converted, directly or indirectly, not only into heat, but also into chemical action in the metamorphic alteration of rock masses. The Plutonic, Neptunic, Quiescent, and Cataclysmic schools of thought, do every one reveal principles which have had a share in nature's operations; and an independent observer finds that the same identical phenomena are at times the result of agencies totally different from those which at other times produced them. For example:

Take crystallised silica, or quartz, it appears

As an igneous product in recent volcanic lavas;

As an aqueous product, by crystallisation and deposition from solution;

As a gasolytic product, in tubes from deposition of its compounds with fluorine.

Molten Sphere and Atmosphere.

Sulphur is seen

As an igneous product from volcanoes;

As an aqueous product from hot springs.
As a product of decomposition of sulphides.
Numerous other examples might be given.

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In applying chemical principles in explanation of the changes wrought in our globe, we shall not touch upon the asserted early gasiform condition as a nebula in space, nor inquire whether the elements then were in a state of chemical indifference to one another; but deal with the earth in its heated condition of complete liquidity. There would be bodies of two different characters-solid and gasiform; these, by their situation and rotation, would bring about the formation of a molten sphere surrounded by an intensely heated gasiform atmosphere. The affinity of bodies would be different, and their mutual chemical reactions vary considerably, from what takes place at ordinary temperatures; so that our conclusions. are, in great part, hypothetical; those conclusions are as follows:

The molten substances and their atmosphere, would obey the laws of gravity; and arrange themselves in strata, or zones, according to their respective density.

The molten mass would arrange into three grand zones, probably with sub-zones; i. an external crust of highly acid silicates, and probably much free quartz; the bases of silicates being chiefly alumina and potash, with some soda, lime, magnesia, etc. ii. A zone of silicates of more basic character and greater density; the bases being lime, magnesia, alumina, oxide of iron, soda, with minor quantities of potash, etc. iii. A far denser nucleus, containing most of the densest metallic elements; in part, at least, combined with sulphur, arsenic, etc. These zones, formed in the earth, would be of somewhat stable character; those in the atmosphere the reverse; but, at first, the atmosphere, next the earth, would be composed of a dense vapour of compounds volatile only at high temperature-the chloride of sodium, probably, one of the most prominent. Above this, the carbonic acid; then oxygen and

1 See Lecture, in Journal of the Chemical Society, 20th February 1868, by David Forbes.

nitrogen the vapour of water still higher. Afterwards, this arrangement would be gradually obliterated by diffusion; but it is imagined that, before diffusion, this arrangement had considerable influence.

The cooling of such an atmosphere would condense the vapour of salt, and other chlorides, etc., and cover the solid crust of the earth with a solid layer, it is calculated, sufficient to clothe the entire sphere with a coating of some ten feet in thickness. Then the condensed steam would fall in rain, which dissolving greater part of the salt, would form the ocean. The atmosphere would now contain much less oxygen; and the carbon, in form of carbonic acid, would probably not differ much in composition from what it is now. The exact action, and extent of reaction; the amount of any one element entering into any particular state of combination, cannot be defined. We may say, however, because the earth is so little flattened, it must have been rotating, when it became solid, at nearly the same rate at which it is now rotating. If we add, as the rate of rotation is undoubtedly becoming slower, it became solid not many millions of years since; otherwise, it would certainly have solidified into a flatter shape; we arrive at the conclusion that we cannot allow geologists a greater possible period than about ten or fifteen millions of years.

There are arguments against these views; we will not advance them. Reference to the lecture on chemical geology, by David Forbes, delivered before the fellows of the Chemical Society, 20th February 1868, and to be found in the Journal of the Society for 1868, p. 213, will afford their refutation.

The mean specific gravity of the earth is 5'4; leaving out the water, the mean density of the exterior is not higher than 275 or 3; it follows that the interior is immensely more dense than the exterior. The crust, at first, might present a somewhat even contour; but soon would be crossed by cracks and fissures, caused by contraction of the mass, and portions of the crust would fall in; then protrusions of molten matter formed dykes on the surface. The sides of the cracks being more or less dislocated, lines of faults would interrupt the previously regular contour, and form the first elevations. or mountains.

From that time till the present all the

Action by Organic Life.

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changes have been wrought, it is considered, by agencies similar to those now in operation. The crust, split and broken, would be further broken and pulverised by the mechanical action of water; assisted by the disintegrating and decomposing action of the carbonic acid, excessively present in the primeval atmosphere; and thus, in process of time, the actions of rivers and seas arranged the comminuted particles in sedimentary beds of varying density and character.

The development of organic life, at first of the lowest type, originated another character of deposits. Vegetation, assimilating the carbonic acid of the atmosphere, introduced beds of carbonaceous substance; and animals and plants, by joint operation, built up the limestones and calcareous strata. The formation of these strata did not proceed uninterruptedly: outbursts of igneous matter disturbed and broke the surface, forming dykes, ramifications, bosses, and sometimes intercalations between the beds. Showers of ashes were also sent forth from time to time. Any geological primer will explain the nature of the igneous, aqueous, and organic rocks. Human intelligence can assign a relative age for every one, and state when the plains and mountains were formed. The various strata are not necessarily separated by vast intervals of time, and the discovery of a universally existing microscopic vegetation shows, that by agency of the lowest and simplest organisms, our globe might be covered, and probably was covered, with all the chief strata.

For illustration of the history as to rocks, taking up a piece of granite, we discover that it was once molten within the earth. Finding a sandstone, it teaches us that small pieces of matter were compressed together, hardened, broken, rolled in and by water. If we have a lump of chalk, and gently grate or knead it down in water, we discover it to consist partly of microscopic chambered shells belonging to animals of simple form and life-protozoa. This chalk, with all other rocks containing relics, whether of vegetable or animal existence, belong to what are called "Organic Rocks." Coal is so much vegetation pressed together, and gradually changed into the black substance now used as fuel. In the deep parts

of the Atlantic Ocean millions and millions of little shells, called foraminifera, are being deposited; the remains of starfish, and other creatures also leave their remains; if they continue undisturbed, a vast mass of rock will be formed out of these dead. The hills and dales of Derbyshire and Yorkshire are chiefly formed of limestone: a mass of the crowded remains of little animals which peopled the waters of the sea. These fossils, or remains, generally enable us to know the age and origin of the various and wonderfully arranged strata which form the crust of the earth.

Geologists define the life-time of the earth as Eozoic, dawn of life; Paleozoic, old life; Mesozoic, middle life; and Neozoic, new or modern life. These are also called Primary Epoch, Secondary Epoch, Tertiary Epoch, and Quaternary Epoch. They are apportioned into ages and eras of stratific formation.

The Eozoic time is supposed to represent that very period during which the first land was cooled and solidified from the fiery mass. Its rocks are the deepest and oldest, crumpled and folded in a remarkable manner, and the folds appear to have been formed before the deposit of the rocks next in age. There is inferential evidence, derived from the limestones, graphite carbon, and iron ore, of vegetable life, as there are undoubted remains of animal life, but the mystery of the origin of living things, and the secret of the changes which they underwent, remain hidden. The deepest and oldest existing rock or formation, the Laurentian Gneiss, is made up out of the waste of previous existing rocks, but of those pre-existing rocks we know nothing. The Laurentide Hills, north of the river St. Laurence, are the largest known exposure of this ancient formation. They are more than 30,000 feet in thickness, and occupy an area of about 200,000 square miles. It was formerly thought that the lowest rocks contained no vestiges of life, and were called Azoic, and that the ocean then existing was lifeless; but we have found that the Laurentian contains a gigantic representative of the earliest known life on earth, the Eozoon Canadense, the grandest of its class; flashing upon the scene like Melchisedec, without father, mother, or descent of days, the modern representatives

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