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Show 806 DESCRIPTION OF THE PLATES AND MAP. shire might with propriety have been represented as sea, if our information respecting the geology of that country had been more full and accurate; for marine shells have been found in sand and gravel at the height of one thousand feet above the level of the sea, on the summit of Moel Tryfane, between Snowdon and the Menai Straits. The species are apparently recent, but certainly are newer than the older tertiary epoch ''k-. The introduction of a small bay where the river Ribble enters into the sea in Lancashire, is warranted by the newly discovered deposit of tertiary shells covering an area of about thirty miles square in that region t. A portion also of the primary district in Brittany is divided into islands, because it has been long known to be covered with patches of marine tertiary strata; and when I examined the disposition of these, in company with my friend Captain S. E. Cook, R.N., in 18SO, I was convinced that the sea must have covered much larger areas than are now occupied by these small and detached deposits. The former connexion of the White Sea and the Gulf of Finland is proved by the fact that a broad band of tertiary strata extends throughout part of the intervening space. We have represented the channel as somewhat broader than the tract now occupied by the tertiary formation, because the latter is bordered on the north-west by a part of Finland, which is extremely low, and so thickly interspersed with lakes as to be nearly half covered with fresh-water. Certain portions of the north-western shores of Norway have been left blank, because the discovery by Von Buch, Bronaniart, and others, of deposits of recent shells along the 0 • coast of Norway and Sweden, at several places and at varwus heights above the level of the sea, attest the comparatively * Joshua. Trimmer, Esq., Proceedings of the Geological Society of London, No. 22, 1831. The shells were exhibited at the Geological Society when the memoir was read. t See an abstract of a memoir read by Mr. Murchison, Pres. Geol. Soc., Pro-ceedings of York meeting, 1831. DESCRIPTION OF THE PLATES AND MAP. 307 recent date of the elevation of part of the gneiss and other primary rocks in that country, although we are unable as yet to determine how far the sea may have extended. On the other hand, a considerable space of low land along the shores of the Gulf of Bothnia, in the Baltic, is represented as sea, because the gl'Owth of deltas on that coast, and the shallowing of the water by sedimentary deposits durina the historical era, leave no room for doubt that the extent :f the gulf must have been very much greater at some periods since the older tertiary epoch. The low granitic steppe coloured red, to the north of the Black Sea has not been represented as having been under water during the tertiary period, although, from the quantity of marine tertiary strata in the surrounding districts, it is far from improbable that it has recently emerged. We were anxious, in the observations annexed to the title of this map, to guard the t·eader against the supposition that it was intended to represent the state of the physical geography of part of Europe at any one period. It is not a restoration of a former condition of things, but a view of the change which a certain amount of surface has undergone within a given period, an alteration so complete, that not one of the species of organic beings which now inhabit the large space designated by ruled lines, beyond the borders of the existing seas, can have lived there during some other period subsequent to the commencement of the tertiary era. We have stated, in the first volume*, that the movements of earthquakes occasion the subsidence as ,vell as the upraising of the surface; and that, by the alternate rising and sinking of particular spaces, at successive periods, a great area may have been entirely covered with marine deposits, although the whole may never have been beneath the waters at one time; nay, even though the relative proportion of land and sea may hav~ con~inued unaltered throughout the whole period. We believe, however, that since the commencement of the tertiary • Page 126. |