Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/416

Rh prevalence of severe climatal conditions through a great part of the northern hemisphere, and during which those marine accumulations, in part truly sedimentary deposits, which have been called "Northern drift," were formed. I have selected the word "glacial," in order to remind the geologists of the ice-charged condition of our seas during that epoch,—conditions which probably did not prevail during its earlier stage, and the gradual disappearance of which marked its conclusion. As, however, it appears almost certain that the "Glacial epoch," and that of the deposition of Sicilian and Rhodian tertiaries were synchronic it would be advisable to adopt some term to express that geological period as a whole, and by which to designate the formations of that period. Mr. Lyell's term, "pleistocene," would, perhaps, best serve the purpose, as that of "newer pleiocene" is not sufficiently distinctive, and may lead to confusion. In this case, among English tertiaries, the coraline crag would rank as meiocene, the red crag as pleiocene, the glacial beds as pleistocene, and the megaceros freshwater marls and marine raised beaches as two stages of post-tertiary.

The line of argument I have adopted is equally applicable to the investigation of the relations, geological and palæontological, of the ancient geological epochs, one with another, as of the present with the geological past. If the constancy of species, and the mutual relationship through a common descent, of all the individuals composing each, be granted, this diffusion in time and space will, when traced, furnish us with a new clue to the determination of the configuration of land and water, during the epochs when they existed, and also to the extension or limitation of peculiar climatal conditions, during each period, and to the causes which replaced them by others.