EUROPE DURIXG THE GLACIAL PERIOD. 449 



hills of Gal way and Mayo at &,000 feet. Its southern limit in 

 Britain is uncertain. According to Professor Ramsay and Dr. 

 James Geikie, it extended as far south as the latitude of Lon- 

 don , but the hypothesis upon which this southern extension 

 is founded — that the bowlder- clays have been formed by ice 

 melting on the land — is open to the objection that no similar 

 clays have been proved to have been so formed, either in the 

 arctic regions, where the ice-sheet has retreated, or in the dis- 

 tricts forsaken by the glaciers in the Alps or Pyrenees, or in 

 any other mountain-chain. Similar deposits, however, have 

 been met with in Davis Strait and in the North Atlantic, 

 which have been formed by melting icebergs ; and we may, 

 therefore, conclude that the bowlder-clays have had a like 

 origin. . . . The English bowlder-clays, as a whole, differ 

 from the moraine profonde in their softness and the large area 

 which they cover. Strata of bowlder-clay at all comparable 

 to the great clay mantle covering the lower grounds of Britain 

 north of the Thames are conspicuous by their absence from 

 the glaciated regions of central Europe and the Pyrenees, which 

 were not depressed beneath the sea.* 



Professor Lewis's views are of such interest that our treat- 

 ment of the subject would be incomplete without a fair pre- 

 sentation of them, which can best be done in his own words : 



The great ice-sheet which once covered northern England 

 was found to be composed of a number of glaciers, each of 

 which was bounded by its own lateral and terminal moraines. 

 These glaciers were studied in detail, beginning with the east 

 of England ; and the North Sea Glacier, the Wensleydale Gla- 

 cier, the Stainmoor Glacier, the Aire Glacier, the Irish Sea 

 Glacier, and the separate Welsh glaciers were each found to 

 be distinguished by characteristic bowlders, and to be defined 

 by well-marked moraines. The terminal moraine of the North 

 Sea Glacier, filled with Norwegian bowlders, may be seen in 

 Holderness, extending from the mouth of the Humber to 

 Flamborough Head, and consists of a series of conical hills 

 inclosing meres. The moraine of the Stainmoor Glacier, char- 



Early Man in Britain," pp. 116, 117. 



