116 EAELY MAN IN BRITAIN. [CHAP. v. 



rocks. In some cases, as near Liverpool, these grooves 

 are found near the present sea-level, and in others they 

 pass far below it. It is very probable that the ice may 

 have arrived at the Atlantic shore at a considerable 

 distance from the present coast-line, and that it may 

 have been continuous with that of Scandinavia, where 

 similar traces have been met with. 



The ice at this time was sufficiently thick to over- 

 ride Schihallion in Perthshire at a height of 3500 

 feet, 1 and the hills of Galway and Mayo at 2000 feet. 2 

 Its southern limit in Britain is uncertain. According 

 to Professor Kamsay and Dr. James Geikie it extended 

 as far south as the latitude of London: but the hypothesis 

 upon which this southern extension is founded that 

 the boulder 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 districts forsaken by the glaciers in the Alps 

 or Pyrenees, 3 or in any other mountain chain. Similar 

 deposits, however, have been met with in Davis Straits 

 and in the North Atlantic, which have been formed by 

 melting icebergs, and we may therefore conclude that the 

 boulder clays have had a like origin. 



To this ice- sheet may be referred the groovings in 

 the rocks underlying the lowest boulder clays of Britain 

 and Ireland, as well as the lines of erratics which some- 

 times can be traced in directions not coinciding with the 

 present valleys, as, for example, those at Norber, near 



1 Jamieson, Quarterly Journal of Geological Society, Lond., xxi. p. 165. 



2 Kinahan and Close, General Glaciation of lar-Connaught and its Neigh- 

 bourhood, Dublin, 1872, p. 16. 



3 See Bonney, Geological Magazine, ii. Vol. iii., " Some Notes on Glaciers." 



