Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/389

376 I have already mentioned that in the glacial deposits the existence of the first of these regions in depth—the littoral zone—is well marked by the surest evidence—the presence of species of Littorina in situ. Having thus got a definite point of the greatest possible amount of shallowness, let us see what evidence those deposits offer of depth. That in no case, so far as I have examined, the upheaved strata were formed under conditions of considerable depth, such as my region of deep-sea corals now presents, is rendered almost certain by the total absence of the remains of the characteristic inhabitants of that region. This could not have been owing to the decay of such remains, for the persistency of the characteristic deep-sea corals of our own and the Arctic Seas, is, from their compactness and size, greater than that of any of the mollusks which have been preserved. We find no traces in these deposits, for instance, of the great Oculina prolifera, still living in the depths of the Zetland Seas and off the coast of Norway; nor of the characteristic Turbinolia, Caryophylleæ, Celleporæ, and smaller corals; nor of the great northern Asteroids, such as Primnoa lepadifera and Alcyonium arboreum, which, from their gigantic size, being equal in dimensions to small trees, would certainly have left some evidence of their existence behind. Instead of these, we get an association of species, which, if we proceed sufficiently far north, we may still find living in the shallows of colder seas, and the greater number of them within the range of the three first regions of our own.

We have a right, then, to infer that the associations of testacea observed in the British glacial deposits, present a northern or arctic aspect as compared with our existing marine fauna, not owing to conditions of greater depth prevailing during the epoch of their existence, but owing to a general colder climate affecting the area within which they are found, and due to causes not now in operation within that area. As these beds in Britain probably approached the southernmost bounds in Europe of the true glacial formation, the regions more to the north in which similar beds are found with similar fossils, must have been formed under similar, and, judging from the greater paucity of species of organic remains in them as compared with the numbers in the British beds, probably severer climatal conditions. So far as I have seen, there is no British case of an upheaved stratum of the glacial formation containing organic remains evidently untransported, which may not have been formed at a less depth than 25 fathoms, and as the Nullipora occasionally occurs in the deeper beds—to which belong most of the clays and marls—it is probable that between 10 and 15 fathoms would more frequently approach the truth. Over a great part of the areas occupied by these glacial beds, we find the uppermost portion composed of sand and gravel, containing fossils more