Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/397

384 deep sea through the upheaved parts of that area, but on the contrary, that very generally it was a shallow sea which then prevailed, one, judging, from the organic remains, not probably beyond 15 fathoms or so deep. This the occurrence of Nullipora in the parts presenting greatest appearances of depth shows, and beds containing deep-sea Arctic species are nowhere exposed. Besides which we have, as has been already shown, distinct evidence of the coast lines of that epoch. Yet fossils, and those too, not littoral species, occur at very high levels, as for instance in Mr. Trimmer's famous case of Moel Trefaen, in North Wales, where beds of gravel and sand containing glacial marine testacea occur at a height of 1,500 feet above the present sea level. These fossils are deposited in the museum of the Geological Society, where I have lately examined them carefully with a view to see whether they indicate an ancient coast line and beach, or an ancient sea-bottom. But they cannot be regarded as indicating either, being a confused mixture of fragments of species from all depths, both littoral and such as invariably live at a depth of many fathoms—of such species as Astarte elliptica, Mytilus edulis, Tellina solidula, Cardium edule, Venus gallina, Buccinum undatum, Mactra solida, Dentalium entalis, Cyprina islandica and Turritella terebra, inhabitants, some of muddy grounds, some of sandy, some of rocky. Deep and shallow water species mingled could at no time have lived together, or have been thrown up on one shore. They indicate the action of some disturbing influence—of having been accumulated far above the level of the then existing sea, through the agency of an iceberg, as suggested by Mr. Darwin, or through the agency of a wave of translation, such as Sir Roderick Murchison has shown to play so important a part in producing the phenomena of the Scandinavian and Russian drifts; or possibly by the combined action of both causes. That such propelling forces derived from afar, were powerful agents of disturbance at the period under consideration, is also rendered probable by the fact that the chief localities of stratified glacial beds, containing undisturbed testacea evidently in situ—as, for instance, great beds of Pecten islandicus, Panopæa arctica, and even such delicate forms as Nuculæ Tellinæ, and Lucinæ in the position in which they lived, and with both valves connected, are to be found in the Clyde districts (where this fact was noted by Mr. Smith) in localities sheltered to the north by mountain ridges which were anciently islands in the glacial sea. These islands had saved many tracts of sea from the disturbing influences of icebergs, and great advancing waves, the course of which, from the north, is indicated by the protected beds; for it is worthy of note that the glacial beds in the northern districts of Scotland, which had no such protecting barriers to defend them—as, for instance, those at Wick—present the same disturbed and unstratified