THE LAST GREA T BA L TIC GLA CIER 327 



towards northeast, north, and, eventually, northwest. South of 

 the Firth, on the other hand, the direction of glaciation is south- 

 erly. In a word, it is demonstrable that during the formatio?i of 

 the 2ipper bozvlder clay the British ice did not follow its 7iat7iral course 

 a7id flozv directly outwards into the basin of the North Sea. It was 

 deflected fust i?i the sajne zvay as the earlier itdand ice of the Saxo?na7i 

 stage had been. So far, indeed, as Scotland was concerned, the 

 ice-sheet of Polandian times was hardly less important than its 

 predecessor. 



The upper bowlder clay is the chief glacial accumulation in 

 our lowlands, and its surface is often concealed under more or 

 less continuous sheets of gravel and sand, while here and there 

 it is dotted over with large erratics and traversed by eskers. 

 All these obviously belong to the period of melting. Nowhere, 

 however, is a vestige of terminal moraine encountered' until the 

 base of the uplands and mountains is approached. Here well- 

 developed terminal moraines suddenly put in an appearance — 

 the relics of large valley -glaciers and local or district ice-sheets. 

 For a long time the general belief was that these moraines had 

 been accumulated during the retreat of the last general ice- 

 sheet (Polandian). Further investigation, however, proved that 

 the outermost moraines had been laid down by advancing gla- 

 ciers, which had everywhere ploughed into the upper bowlder 

 clay, sweeping it out of the valleys, and so modifying its surface 

 in the low grounds at the base of the mountains as to impress 

 upon it a new configuration. The dimensions of the moraines, 

 the extent of their fluvio-glacial gravels, and the amount of 

 erosion experienced not only by the upper bowlder clay, but by 

 the solid rocks themselves, all indicate that these valley-glaciers 

 and local ice-sheets mark a distinct stage of the Glacial Period. 



Again, there is evidence to show that after the retreat of the 

 ice-sheet of the upper bowlder clay, and before the valley-gla- 

 ciers in the west of Scotland had descended to the coast, the 

 maritime districts were slightly submerged. Loch Lomond 

 at that time formed an arm of the sea, and was tenanted by a 

 fauna which consisted for the most part of existing British forms. 



