But the changes going on at the surface were only symptomatic of those occurring beneath. The immense accumulations of Silurian sediment had by this time so overweighted certain portions of the crust, that great quantities of aqueous sediment had been pressed downward into the heated bowels of the earth, and were undergoing, under an enormous weight of superincumbent material, a process of baking and semi-fusion. This process was of course extremely active along the margins of the old Silurian plateaus, and led to great elevation of land, while in the more central parts of the plateaus the oceanic conditions still continued; and in the Middle Devonian, in America at least, one of the most remarkable and interesting coral limestones in the world--the corniferous limestone--was deposited. In process of time, however, these clear waters became shallow, and were invaded by muddy sediments; and in the Upper Devonian the swampy flats and muddy shallows return in full force, and in some degree anticipate the still greater areas of this kind which existed in the succeeding Coal formation. Such is a brief sketch of the Devonian, or, as it may be better called in America, from the vast development of its beds on the south side of Lake Erie, the _Erian_ formation. In America the marine beds of the Devonian were deposited on the same great continental plateau which supported the seas of the Upper and Lower Silurian, and the beds were thicker towards the east and thinned towards the west, as in the case of the older series. But in the Devonian there was much, land in the north-east of America; and on the eastern margin of this land, as in Gaspé and New Brunswick, the deposits throughout the whole period were sandstones and shales, without the great coral limestones of the central plateau. Something of the same kind occurred in Europe, where, however, the area of Devonian sea was smaller. There the fossiliferous limestones of the Middle Devonian in Devon, in the Eifel district, in France and in Russia, represent the great corniferous limestone of America; while the sandstones of South Wales, of Ireland, and of Scotland, resemble the local conditions of Gaspé and New Brunswick, and belonged to a similar area in the north-west of Europe, in which shallow water and land conditions prevailed during the whole of the Devonian, and which was perhaps connected with the corresponding region in Eastern America by a North Atlantic archipelago, now submerged. This whole subject is so important to the knowledge of the Devonian, and of geology in general, that I may be pardoned for introducing it here in a tabular form, taking the European series from Etheridge's excellent and exhaustive paper in the "Journal of the Geological Society." DEVONIAN OF ERIAN. DIVISIONS. CENTRAL AREAS. Devon. Rhen. Prussia. New York.