appearance of some of the formations which would indicate a chemical deposition, which may have taken place in a comparatively short time, and to a considerable extent of thickness, under the combined actions of heat and aqueous mixture. This is particularly remarkable in the chalk; the extreme uniform minuteness of its particles, the unmixed purity of its composition, its loose and slightly coherent texture, and its cavities filled up with concretions of siliceous matter, all pointing out a chemical more than a mechanical deposition.

Perhaps the same conjecture may be applied to the magnesian limestone, and extended, with some degree of probability, to portions, at least, of the oolitic strata.

That the gypsum and salt beds of the new red sandstone indicate chemical action, is also apparent, while the position of the accompanying strata of sandstone and conglomerate, shew considerable transportation and accumulation of their materials.

Finally, the sedimentary strata, even in their greatest thickness, constitute but a very small proportion of that part of the globe elevated above the level of the ocean. The igneous rocks formed in the bowels of the earth, and thrust upwards by volcanic convulsions, make up by far the greatest part of the mass of our continents and islands. These rocks are only visible as they constitute mountain chains, and occasionally as they break

through the superincumbent strata ; but their existence is no less demonstrable in our level plains and undulating valleys. In fact, the lowest and most horizontal strata must have been raised to their present position above the level of the sea by the agency of such igneous masses. It is not necessary that we should here inquire into the causes of these elevations ;* but it is now admitted on all hands that operations, corresponding, in an intimate degree, with modern volcanic actions, were at work in their production. The extent of these ancient mountain chains, the manner in which they appear to have elevated the strata of whole islands and large portions of continents, by one continuous and uninterrupted process, seem, however, to indicate, that though the causes were similar to volcanic, yet that the amount of the forces and the extent of the operations were in an infinitely greater degree, and much more general, than any witnessed in modern times.

That repeated elevations of this nature have occurred at very distant intervals, is quite evident from the appearances of the disrupted strata; and from indications in this strata, certain relative periods of convulsion can be distinctly pointed out. Thus, an early eruption has evidently elevated the primary or oldest gneiss and mica slate

* Note III.

systems. Another eruption has occurred at the period of the greywacke deposition, and a third posterior to the formation of the coal strata; and these operations are continued, and brought down even to the present period of volcanic action.

But the very aspect of the various kinds of igneous rocks shews that they were formed under different circumstances. Thus granite differs from the porphyries and greenstones; and these again, in some degree, from the more recent lavas, shewing that a varying degree of superincumbent pressure, or of intensity of force, or magnitude of the masses in action, may have thus taken place at the successive periods of their production. Because the elevating power of modern volcanoes, then, is a slow and gradual process, to maintain that the more ancient eruptions must also have occupied a lengthened period, is a conclusion which, taking all the circumstances into consideration, cannot be admitted,

41

SECTION V.

SUCCESSIVE SERIES OF ORGANIC REMAINS IN THE

DIFFERENT FORMATIONS.

THE next argument in support of the great antiquity of the earth, is the successive series of animal and vegetable remains peculiar to each of the fossiliferous strata. For it is supposed, that not only in each of the leading formations, but in many cases in each subordinate bed of such formations, peculiar kinds of organized beings have flourished for an epoch, and then disappeared, to be succeeded by a fresh creation of animal and vegetable existences. Now, it cannot be denied that such a gradation of fossil remains does exist, though extended discovery is daily making innovations on the various theories of their classification, and the deductions too hastily drawn from isolated facts. Yet we shall assume, that, generally speaking, each formation is characterized by peculiar fossils.

In considering this subject, we must leave out of view the original creation of organized

beings, as a matter utterly beyond our comprehension, and consequently without the field of our reasoning. But, looking on nature as it exists, we see no power or tendency in her works to produce organized existences from inorganic matter, neither have we any facts to shew that new species can be propagated and continued from existing organic life. On the contrary, a definite law of nature confines the production of new beings to a parent of the same species. It cannot be urged that time is necessary for the development of this phenomenon: did the law or tendency exist, it would most assuredly operate continually. Seeing, then, that there are no facts or analogies in nature to support the idea of a successive creation of species, it is unphilosophical to extend such an assumption to the past period of the earth's history.* That many species of plants and animals which once existed may have become extinct, however, is a circumstance which readily admits of illustration. Thus, partial extirpations of animals are taking place in every country as the numbers of mankind increase, and changes are brought about on the surface of the soil. The wolf, the beaver, and some kinds of deer, have entirely disappeared from Britain within the last few centuries; and the dodo is a well known example of a bird extirpated from

* Note IV.