680 MR DAVID MILNE HOME ON THE BOULDER-CLAY OF EUROPE. 



shells occur in the pleistocene beds of Lanarkshire, at a height of 526 feet above 

 the sea ; and as one of these shells is the Cyprina islandica, which requires for 

 healthful existence a depth of at least 30 fathoms, that Lanarkshire deposit 

 implies a submergence of more than 700 feet. 



But in Wales, sea-shells of a similar character have been found in drift- beds 

 at a height of no less than 1600 feet above the sea. And there are in many parts 

 of England and .Scotland beds of clay, sand, and gravel, at a height of nearly 

 2500 feet above the sea, which, judging from their stratification and materials, 

 must have been marine. 



If, therefore, the whole of the British Islands were submerged to the depth of 

 2500 feet lower than they are at present, they must have presented little else 

 than an archipelago of islands, — few of which would, at their highest points, be 

 more than 1500 feet above the sea. 



As many of the shells found in these pleistocene beds are of an exclusively 

 Arctic type, the sea, during the period of submergence now referred to, was 

 favourable for the presence of drifting ice, — assuming, in the meantime, the 

 existence of some current to bring the ice. 



But it is not Great Britain only which was submerged. In Sweden, sea-shells 

 of the same Arctic type have been found in drift-beds to the height of 800 feet, 

 there being also beds, apparently marine, which occur at a still greater height. 



These Swedish shell-beds have furnished one or two instructive facts bearing 

 on the process of submergence, which probably apply to Northern Europe gene- 

 rally. Some of the beds are occupied almost exclusively by shells which lived in 

 shallow water. These are in some places covered by beds containing shells of 

 deep-water habits, — indicative not only of a submergence of the country, but a 

 submergence to a considerable extent. Farther, it has been ascertained that 

 these deep-water shells belong to much more Arctic types than those of shallow 

 water which preceded them, — indicating that as the submergence went on, the 

 cold was increasing. Then, again, other shell-beds have been discovered at a 

 lower level, and evidently, from their geological relations, of a more recent date 

 than those above mentioned, in which the Arctic shells are fewer in number and 

 species, — a fact which suggests that, as the land emerged from beneath the 

 waters, the climate improved.* 



It is, however, not in Sweden only that these Arctic shells are found on the 

 Continent. Sir Boderick Murchison, in his great work on the Geology of Russia, 

 has shown that the drift-lands of that country are full of them, implying a 

 general submergence of the whole of Northern Europe under the waters of an 

 Arctic sea, reaching as far south as about latitude 51°. 



* These interesting and instructive facts will be found stated in a Memoir, by Mr Gywn 

 Jeffreys, in the British Association Reports for 1863 ; and also in a paper, bj Professor Sars of 

 Christiania, in the Edinburgh Phil. Journal for 1863. 



