THE GLACIAL PERIOD. 187 



brown tint, and acquires a redder hue, which by and by deepens 

 into a red as pronounced as that of the Old Bed Sandstone 

 itself. Owing, however, to the superior hardness of the Silurian 

 fragments, which could resist crushing and grinding much more 

 effectually than the softer sandstones, the boulders derived from 

 the regions above Galashiels are always present in large num- 

 bers. As we continue on our way down the valley we pass numer- 

 ous knolls, hills, and wider sheets of various igneous rocks, and 

 no sooner do we pass one of these than fragments of it appear 

 in the till. Search the whole wide valley from its source to 

 its termination, and we shall not find a single example of a 

 boulder -clay stone which has travelled up the valley, or in 

 any other direction than that followed by the trend of the 

 striae and the drums. And the same holds true of every region 

 in Scotland. 



There are many other facts connected with the stones in the 

 till, and which all point to the same conclusion, namely, that the 

 till is the bottom-moraine of the old ice-sheet ; but these I need 

 not discuss in this place. I may merely refer in a word to the 

 occurrence here and there, in and underneath the till, of patches 

 and irregular layers and beds of coarse shingle, large boulders, 

 earthy angular or sub-angular gravel, waterworn stones, sand, 

 and laminated clay — all these point to the fact that during the 

 accumulation of the till water circulated to some extent under- 

 neath the ice. The deposits in question mark the sites of 

 sub-glacial channels and lakelets which formed from time 

 to time, and were doubtless often shifted by movements in 

 the ice overhead. This is shown by the manner in which 

 the beds are usually abruptly cut asunder, contorted, con- 

 fused, bent back upon themselves, and even frequently coiled 

 up and involved with the till in such a way as to prove 

 that they have been rolled forward with the boulder -clay 

 en masse. 



In remarking upon the fact that the direction of movement 

 of the Scottish ice -sheet was determined by the form of the 

 ground, I referred to a great deflection of ice -flow caused by 



