CHAP, vir THE GLACIAL EPOCH 113 



rocks many feet in diameter. The " till" is found chiefly 

 in the low-lying districts, where it covers extensive areas 

 sometimes to a depth of a hundred feet ; while in the 

 highlands it occurs in much smaller patches, but in some 

 of the broader valleys forms terraces which have been cut 

 through by the streams. Occasionally it is found as hio-h 

 as two thousand feet above the sea, in hollows or hill-sides, 

 where it seems to have been protected from denudation. 



The " till " is totally unstratified, and the rock-surfaces 

 on which it almost always rests are invariably worn smooth, 

 and much grooved and striated when the rock is hard ; 

 but when it is soft or jointed, it frequently shows a greatly 

 broken surface. Its colour and texture, and the nature of 

 the stones it contains, all correspond to the character of 

 the rock of the district where it occurs, so that it is clearly 

 a local formation. It is often found underneath moraines, 

 drift, and other late glacial deposits, but never overlies 

 them (except in special cases to be hereafter referred to), 

 so that it is certainly an earlier deposit. 



Throughout Scotland, where " till " is found, the glacial 

 striae, perched blocks, rochcs moutonn^es, and other marks 

 of glacial action, occur very high up the mountains to at 

 least 3,000 and often even to 3,500 feet above the sea, 

 while all lower hills and mountains are rounded and 

 grooved on their very summits ; and these grooves always 

 radiate outwards from the highest peaks and ridges towards 

 the valleys or the sea. 



Inferences from the Glacial Phenomena of Scotland^ — Now 

 all these phenomena taken together render it certain that 

 the whole of Scotland was once buried in a vast sea of ice> 

 out of which only the highest mountains raised their 

 summits. There is absolutely no escape from this con- 

 clusion ; for the facts which lead to it are not local — found 

 only in one spot or one valley — but general throughout 

 the entire length and breadth of Scotland ; and are besides 

 supported by such a mass of detailed corroborative evidence 

 as to amount to absolute demonstration. The weight of 

 this vast ice-sheet, at least three thousand feet in maxi- 

 mum thickness, and continually moving seaward with a 

 slow grinding motion like that of all existing glaciers, 



I 



