when the north of Europe had already assumed that remarkable feature of its physical geography, which separates the Baltic from the North Sea, and causes the Gulf of Bothnia to have only one-fourth of the saltness belonging to the ocean.
I cannot doubt that these large erratics of Upsala were brought into their present position during the recent period, not only because of their moderate elevation above the sea-level in a country where the land is now rising every century, but because I observed signs of a great oscillation of level which had taken place at Södertelje, south of Stockholm (about forty-five miles distant from Upsala), after the country had been inhabited by man. I described, in the 'Philosophical Transactions' for 1835, the section there laid open in digging a level in 1819, which showed that a subsidence followed by a re-elevation of land, each movement amounting to more than sixty feet, had occurred since the time when a rude hut had been built on the ancient shore. The wooden frame of the hut, with a ring of hearthstones on the floor, and much charcoal, were found, and over them marine strata, more than sixty feet thick, containing the dwarf variety of Mytilus edulis, and other brackish-water shells of the Bothnian Gulf. Some vessels put together with wooden pegs, of anterior date to the use of metals, were also embedded in parts of the same marine formation, which has since been raised, so that the upper beds are more than sixty feet above the sea-level, the hut being thus restored to about its original position relatively to the sea.
We have seen in the account of the Danish 'shell-mounds,' or 'refuse-heaps', of the recent period (p. 13), that even at the comparatively late period of their origin the waters of the Baltic had been rendered more salt than they are now. The Upsala erratics may belong to nearly the same era as those 'refuse-heaps.' But were we to go back to a long antecedent epoch, or to that of the Belgian and British caves with their
