Page:The Journal of geology (IA journalofgeology21894univers).pdf/215
the Urals, probably in Sumatra, and in Arkansas. The genus Pronorites, while found in western Europe, is rare in it, and is much more common in the Pacific region. Pronorites is found in the Artinsk region and in Arkansas, while the ammonite genus Medlicottia, the direct descendant of Pronorites, is found in the Permo-Carboniferous strata of Sicily, the Urals, the Salt Range, and Texas.
It is impossible to suppose that the same genus and species originated at different localities, and since we have both ancestors and descendants in places so widely separated, we can only suppose that there was free interchange of life between those places at that time, or in other words an open sea, on the borders of which these fossiliferous deposits were laid down, and through which the cephalopods and other marine animals could migrate.
Replacement of Limestones by coal-bearing formations in western Europe.—On tracing the Upper Carboniferous deposits of the Ural region towards the west, we find the limestones thinning out, and the Coal Measures and Culm formations taking their places; we find also that the transgression of marine on terrestrial deposits takes place from the east, just the reverse of what is seen in America.
Land areas in the West.—It is not thought that the Pacific Carboniferous sea was an unbroken expanse of water in western America; on the contrary there are many evidences of large isolated land areas and archipelagos.
Dr. Joseph Le Conte[1] has argued that the Basin Range, during much of Paleozoic and Mesozoic time, was a continent, off the western shores of which the sediments that afterwards became the Sierra Nevada and Coast Range were laid down. Clarence King[2] thought that the great thickness of Paleozoic littoral deposits in the Great Basin region proved the existence of a large body of land further west; he thought that the eastern shore of this continent was in Nevada, and east of this stretched the Carboniferous sea, which covered all but the island chain of the Rocky moun-