Page:A Treatise on Geology, volume 1.djvu/30

 14 even brought from small distances to be so buried, yet the inference is little altered by these admissions; for still, between the formation of certain beds, above and below those shells, their lifetime must have passed.

But these conclusions become at once strengthened and more definite when we take into consideration the nature of the series of these terms; each of which indicates the lapse of time. For, first, it is found that the terms are recurrent, so that again and again similar or analogous strata are repeated, in different combinations, proving that the physical conditions which governed these depositions of strata were in some respects of periodical occurrence, or rather subject to interruption and fluctuation, so that different combinations prevailed at different periods. If we ask, in modern nature, so uniform in the local results of the same kind, the explanation of this, the reply will be immediately found: those periods of new combinations among the physical conditions of a given region are far beyond the range of human experience.

Moreover, an additional fact of great interest here comes to fortify all our inferences—the organic remains of plants and animals which abound in the earth are not those of the tribes that now live, but of many wholly extinct, and often quite different, races—different in form and structure, and, consequently, in function and habits of life, though certainly belonging to a general system of nature founded on analogous principal conditions. Further, it is not sufficient nor correct to say, there is one living and one extinct creation: the plants and animals buried in the earth belong to many distinct and successive creations, which differ among one another no less than they almost all differ from the actual forms of life. These distinct creations of former date are found buried in different parts of the series of strata; one series of organic forms belongs to