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] [13] See M. Pictet's "_Palæontologie_." Tertiary Epochs. An extensive series, comprising many isolated groups of marine and lacustrine deposits, containing fossil remains of animals and vegetables of all classes; the greater number of genera and species in the most ancient or lowermost beds belong to extinct types. _Subdivisions_:-- 1. The Pliocene[14] (_more new_, or _recent_.[15] _Wond._ p. 221); strata in which the shells are for the most part of recent species, having only about ten per cent of extinct forms. (_Norwich Crag._) 2. The Miocene (_less recent_,[16] _Wond._ p. 221); containing about 20 per cent of recent species of shells. (_Suffolk Crag._) 3. The Eocene (_dawn of recent_,[17] in allusion to the first appearance of recent species--_Wond._ p. 226); the most ancient tertiary strata contain but very few existing species of shells; not more than five per cent. (_London, Hants, and Paris basins._) [14] In the present state of our knowledge, this arrangement is of great utility, but it will probably require considerable modification, and must, perhaps, hereafter be abandoned; for it cannot be doubted, that strata in which no recent species have yet been found, may yield them to more accurate and extended observations, and those in which only a few recent species are associated with a large number of extinct forms, may have these proportions reversed. [15] From πλειων, _pleion_, more; and καινος, _kainos_, recent. [16] From μεἱων, _meion_, less, and recent. [17] From ἠως, _eos_, the dawn or commencement, and _recent_. _Obs._--The marine are often associated with fresh-water deposits, and the general characters of the Tertiary system are alternations of marine and lacustrine strata. In England the most important Tertiary deposits are those of the London basin, the Isle of Sheppey, the south-western coasts of Sussex and Hampshire, the north of the Isle of Wight, and the eastern coasts of Essex, Norfolk, Suffolk. (_Wond._ p. 226.) Secondary Epochs.