Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/396

Rh must have been a shallow sea, and somewhere, probably far to the north, there must have been either a connexion or such a proximity of land as would account for the transmission of a non-migratory terrestrial, and a littoral marine fauna. Such are the indications afforded by zoological evidences: they are, doubtless, closely connected with the history of the climatal changes which terminated the epoch we are considering.

It has been already stated that the remains of testacea through a great part of the glacial or drift-beds, are in a fragmentary or rolled state, and are not distributed in horizons (as they would be if the ground on which they lived had been elevated undisturbed), but are often scattered through confused and unstratified masses of mud and sand or gravel. It has also been stated that this is not everywhere the case: that in certain localities we find the organic remains forming well defined horizons, and in such a state of preservation as to indicate that they lived and died on the spots where they are found; and that among these undisturbed localities we find some which, containing littoral fossils in situ, indicate the lines of coast and tide-mark. These facts suggest two questions: 1st, what were the disturbing influences? and, 2nd, how far are we to regard all drift beds containing marine remains as having been formed beneath the sea, on the spots where they now are found?

So far as I have observed the fossils in the great exposed tracts of northern drifts as in Ireland, the north of England, and the Isle of Man, are generally fragmentary or rolled. Occasionally strata occur in the midst of the beds less disturbed than the greater part of them, and containing shells apparently in situ; but through the greater part of the epoch of their deposition, disturbing influences appear to have been at work throughout the area of the glacial sea. These disturbing influences were probably of two kinds—the phoughing-up action of icebergs, and the sweeping action of great waves coming from the north.

To the first may be attributed the general confused condition of the mud bottoms, and the fragmentary and disturbed state of their included fossils, which are all species, not transported, but occurring in undisturbed localities, in such a state as to prove that they were indigenous to the seas in the upheaved beds of which they are now found.

To the second, the transport to very high levels of masses of marine drift with organic remains, may be referred, either by washing up, high and dry, portions of the sea-bed, or by propelling and stranding masses of ice which, in their turn propelled before them the contents mineral and organic of the sea. For the evidence presented by glacial testacea in situ in all tracts of sufficient extent within the area of the British Isles, shows that at no period during their existence was there a very