THE GLACIAL PERIOD. 179 



smothered in ice, they yet greatly influenced the direction of 

 the ice-flow. As we approach some prominent hill that stood 

 fronting the glacial current, we find the striae begin to change 

 their direction, bending round as it were to escape the obstruc- 

 tion. These hills and the smaller islands appear thus to have 

 played much the same part as large submerged boulders in the 

 bed of a river. They turned aside the ice that beat against 

 them, buried deep though they were beneath the upper surface 

 of the mer de glace. It must be remembered that it is not only 

 level or approximately level surfaces which bear the marks of 

 glacial abrasion. Sloping faces and sometimes even vertical 

 faces are distinctly striated by ice which has been pressed up 

 and over them. Thus the flanks of the Sidlaws and the Ochils, 

 which look towards the Highlands, are grooved and striated by 

 ice which has crossed Strathmore and Strathearn respectively, 

 and thereafter made its way up and over both ranges, forced 

 forward by the ice continually advancing from behind. The 

 direction taken by the ice, therefore, does not always coincide 

 exactly with the configuration of the ground — minor features 

 such as those I have mentioned were practically disregarded, 

 although as already remarked they always influence the trend 

 of the striae in a greater or less degree. The ice streamed out 

 in all directions from the dominating ridges, and thus followed 

 the line of what is still the main drainage of the country. For 

 example, the general direction in the lowlands of Forfar, Perth, 

 and Stirling was towards the south-east. In Linlithgowshire 

 and Midlothian it is more easterly. The mer de glace from the 

 Highlands encountered that which pressed northwards from the 

 Southern Uplands, and thereafter the two streams united to 

 flow east by way of Linlithgow, Midlothian, and Haddington, 

 and south-west across the district that extends from the Clyde, 

 near Hamilton, to the sea at Ayr. Deflections of the main 

 current were thus produced by the conflicting motions of the 

 great mer de glace itself. The most remarkable deflection of the 

 kind, however, still remains to be noticed. But the evidence 

 for this will be better appreciated after I have said something 



