Of the Thurmberg, Humboldt remarks that it is the most remarkable elevation between the Hartz and the Ural Mountains, and that but a few points in the Valdai range can be brought into comparison with it. Its position close by the sea is especially noteworthy. It is very probable, according to Humboldt’s opinion, that those inequalities of surface, formed of sand once partly or wholly submerged,—found in Mecklenberg, Pomerania, East Prussia Proper,—and now divided into flats and hill ranges, do not belong to the dune system of the ancient shore-line, but have the reason of their existence in ordinary upheaval; in the formation of limestone, and of the usual Jurassic rocks, which, afterward, have been covered with sand and other loose materials. The peculiar accumulation of genuine marine fossils indicates the existence of upheaved rocks below the upper layer of sand. It is these elevations which in the constantly advancing ridge or ridges run northeasterly, and take the form of plateaus, increasing in breadth from the water-shed north of Smolensk, and the source of the Dnieper, in the Valdai Forest, and the western Uwalli, and which are found between the Volga and the Dwiner, and thence run eastward as far as Perm, on the Kama. They form the line of demarkation between the great Central European plain and the North Russian lowland, which extends as far up as the Arctic. This easterly chain, so far as it has been measured, seems to be less in altitude than the Valdai hills, which are about 1000 feet high. In East Prussia Proper and Livonia there are elevations of more than 600 feet; about 55 miles south of Dorpat Munnamäggi, the point of culmination, according to Struve, is 996 feet above the sea; south of Vilna the heights of Puzewitch reach an elevation of 990 feet.