of a stronger degree of heat than what operated in subsequent stages of the world, for the laminæ of the gneiss and of the mica and chlorite schists are contorted in a way which could only be the result of a very high temperature. It appears as if the seas in which these deposits were formed, had been in the troubled state of a caldron of water nearly at boiling heat. Such a condition would probably add not a little to the disintegrating power of the

ocean.

The earliest stratified rocks contain no matters which are not to be found in the primitive granite. They are the same in material, but only changed into new forms and combinations; hence they have been called by Mr. Lyell, metamorphic rocks. But how comes it that some of them are composed almost exclusively of one of the materials of granite; the mica schists, for example, of mica-the quartz rocks, of quartz, &c.? For this there are both chemical and mechanical causes. Suppose that a river has a certain quantity of material to carry down, it is evident that it will soonest drop the larger particles, and carry the lightest farthest on. To such a cause is it owing that some of the materials of the worn down granite have settled in one place and some in another.* Again, some of these materials must be presumed to have been in a state of chemical solution in the primeval seas. It would be of course in conformity with chemical laws, that certain of these materials would be precipitated singly, or in modified combinations, to the bottom, so as to form rocks by themselves.

* De la Beche's Geological Researches.

39

COMMENCEMENT OF ORGANIC LIFE-SEA

PLANTS, CORALS, ETC.

FROM the Primary Rocks, we pass into a group called the Clay Slate and Grauwacké Slate System, which, however, is found in some places resting immediately on the granite, the primary bed being there wanting. This system is largely developed in the west and north of England, and it has been well examined, partly because some of the slate beds are extensively quarried for domestic purposes. The sub-divisions are in the following order, beginning with the lowest :-1, hornblende slate; 2, chiastolite slate; 3, clay slate; 4, Snowdon rocks (grauwacké and conglomerates).

Hitherto nothing has been said of the fossils which constitute so important a part of geological science. It is now to be observed that, from an early portion of the rock series to its close, the mineral masses are found to enclose remains of the organic beings (plants and animals) which flourished upon earth during the time when those were forming; and these organisms, or such parts of them as were of sufficient solidity, have been in many cases pre

served with the utmost fidelity, although for the most part converted into the substance of the enclosing mineral. The rocks may be said thus to form a kind of history of the organic departments of nature from perhaps near its beginning to the present time. This is a piece of knowledge entirely new to man, and it may be safely said that he has never made a merely intellectual acquisition of a more interesting or remarkable nature. I am to trace this history as well as existing materials will permit.

Some difficulty exists with regard to the very first chapter of Fauna's story. It is as yet undecided at what part of the rock series we have the earliest traces of the life which exists upon our globe. The primary rocks are usually said to be non-fossiliferous-that is, possessing no remains of plants or animals; and it would appear that the first undoubted objects of a fossil kind are the solid parts of polypiaria, crinoidea, crustacea, and conchifera, found in the Mica Slate and Grauwacké Slate System. These cannot, however, be regarded as for certain the first of earth's tenants, seeing that "fragments apparently organic, and resembling the cases of infusoria [shelled animalcules]"* have been detected in the primary rocks, and it is very clear that many other simple forms of being, such as the medusæ and acalephæ, which now swarm in our seas, might have peopled the early ocean, but left no memorial of their slight gelatinous forms in the mud constituting its bottom, particularly as that mud has evidently been afterwards subjected, in its rocky form, to a great degree of heat. So also might the fragile plants of the primary sea fail to come down to us.

* Ansted's Geology, ii., 60.

We are also called upon to remark the occurrence of a few limestone strata amongst the primary rocks. Limestone, a carbonate of lime, contains an element (carbon) which we have no reason to believe to have existed in the rock from which the primaries were derived. It is a challengeable stranger upon the face of the earth, and extremely important to the present question, in as far as it is the principal constituent of organic substance of almost every kind. Plants take in this substance from the atmosphere, where it is a subordinate ingredient; there are classes of animals (marine polypes), which appropriate it in connexion with lime from the waters of the ocean, provided it be there in solution: and this substance do these animals deposit in masses (coral reefs) equal in extent to many strata. It is fully ascertained of many strata of limestone higher in the series, that they are simply reefs of that kind changed by subjection to heat and pressure. It may be asked, then, does not this series of facts establish a strongly probable connexion between the time of the primary limestones and the earlier days or ages of organic creations?

It may not be out of place here to remark, that the primeval and subsequent history of this element is worthy of much attention. Sir Henry De la Beche estimates the quantity of carbonic acid gas locked up in every cubic yard of limestone, at 10,000 cubic feet. The quantity locked up in coal, in which its basis, carbon, forms from 64 to 75 per cent., must also be enormous. If all this were disengaged in a gaseous form, the constitution of the atmosphere would undergo a change, of which the first effect would be the extinction of life in all the land animals. Yet, if it has all been derived from the atmo

sphere, we must needs suppose that the atmosphere at one time contained it. Such an atmosphere would, of course, be incapable of supporting life in land animals. It is important, however, to observe that such an atmosphere would not be inconsistent with a luxuriant land vegetation; for experiment has proved that plants will flourish in air containing one-twelfth of this gas, or 166 times more than the present charge of our atmosphere. The results which we observe are perfectly consistent with, and may be said to presuppose, an atmosphere highly charged with this gas, from about the close of the primary rocks to the termination of the carboniferous series, for there we see vast deposits (coal) containing carbon as a large ingredient, while at the same time the leaves of the Stone Book present no record of the contemporaneous existence of land animals.

Of the fossils specified as being found in the mica slate and grauwacké slate system, the two first are examples of the humblest of Cuvier's four divisions of the animal kingdom, radiata; while the other two belong respectively to the two next divisions, articulata and mullusca. In common, though not very precise language, they are corals and shell-fish. Nothing uncommon or surprising is to be observed in their forms; but it is remarkable that, though they can readily be referred to existing orders, the species and even genera to which they belonged are no longer found on earth; nay, almost the whole had become extinct before the next group of strata was formed. Such changes of species we shall find to be of frequent occurrence throughout the subsequent ages. To descend to a few particulars:-The crinoids are an early and simple form of the large family of echinodermata (star-fishes);