112 



ISLAND LIFE 



PART I 



view he had first adopted — that the blocks had been 

 carried by floating ice during a period of submergence — as 

 altogether untenable.-^ 



The phenomena now described demonstrate a change of 

 climate sufficient to cover all our higher mountains with 

 perpetual snow, and fill the adjacent valleys with huge 

 glaciers at least as extensive as those now found in Switzer- 

 land. But there are other phenomena, best developed in 

 the northern part of our islands, which show that even 

 this state of things was but the concluding phase of the 

 glacial period, which, during its maximum development, 

 must have reduced the northern half of our island to a 

 condition only to be paralleled now in Greenland and the 

 Antarctic regions. As few persons besides professed geolo- 

 gists are acquainted with the weight of evidence for this 

 statement, and as it is most important for our purpose to 

 understand the amount of the climatal changes the northern 

 hemisphere has undergone, I will endeavour to make the 

 evidence intelligible, referring my readers for full details 

 to Dr. James Geikie's descriptions and illustrations.^ 



Glacial Deposits of Scotland : the " Till" — Over almost all 

 the lowlands and in most of the highland valleys of Scotland 

 there are immense superficial deposits of clay, sand, gravel, 

 or drift, which can be traced more or less directly to 

 glacial action. Some of these are moraine matter, others 

 are lacustrine deposits, while others again have been 

 formed or modified by the sea during periods of sub- 

 mergence. But below them all, and often resting directly 

 on the rock-surface, there are extensive layers of a very 

 tough clayey deposit known as " till." The till is very fine 

 in texture, very tenacious, and often of a rock-like hardness. 

 It is always full of stones, all of which are of rude form, 

 but with the angles rubbed off, and almost always covered 

 with scratches and striae often crossing each other in various 

 directions. Sometimes the stones are so numerous that 

 there seems to be only just enough clay to unite them into 

 a solid mass, and they are of all sizes, from mere grit up to 



1 Antiquity of Man, Ath. Ed. pp. 340-348. 



2 The Great Ice Age and its Relation to the Antiquity of Man. By James 

 Geikie, F.R.S. (Isbister and Co., 1874.) 



