The classification of the stratified rocks is based on three principal characters; namely, 1, the mineral structure; 2, the order of superposition; and 3, the nature of the organic remains; the following synopsis has been drawn up in accordance with these principles.[12]
[12] See "Wonders of Geology," vol. i. pp. 200-207, for a Synoptical Table of the principal rocks.
CHRONOLOGICAL ARRANGEMENT OF THE BRITISH FORMATIONS.
COMMENCING WITH THE UPPERMOST OR NEWEST DEPOSITS.
Alluvial Deposits: remains of Man and existing species of mammalia.
Drift; Boulder clay; Till; &c. comprising the superficial irregular accumulations of transported materials, consisting of gravel, boulders, sand, clay, &c.
Observations.—These beds have been formed by a variety of causes; by land-floods and inundations, by irruptions of the sea, and by the agency of glaciers and icebergs. They are the catacombs of the extinct colossal mammalia—of the mastodon, mammoth, rhinoceros, hippopotamus, elk, horse, ox, whale, &c. They cannot be definitively separated from those of the Modern or Human epoch, for the gravel beds near Geneva, which closely resemble the newest tertiary drift in materials and position, abound in bones of animals, almost all of which belong to existing species.[13]