CHAP. VII.] 



THE GLACIAL EPOCH. 



113 



than in Europe, stretching over the whole of Canada and to the 

 south of the great lakes as far as latitude 39°. There is, in all 

 these countries, a wide-spread deposit like the ''till" of Scotland, 

 produced by the grinding of the great ice-sheet when it was at its 

 maximum thickness ; and also extensive beds of moraine-matter, 

 true moraines, and travelled blocks, left by the glaciers as they 

 retreated towards the mountains and finally withdrew into the 

 upland valleys. There are, also, both in Britain, Scandinavia, 

 and North America, proofs of the submersion of the land 

 beneath the sea to a depth of upw^ards of a thousand feet ; but 

 this is a subject we need not here enter upon, as our special 

 object is to show the reality and amount of that wonderful and 

 comparatively recent change of climate termed the glacial epoch. 



Many persons, even among scientific men, who have not given 

 much attention to the question, look upon the whole subject of 

 the glacial epoch as a geological theory made to explain certain 

 phenomena which are otherwise a puzzle ; and they would not 

 be much surprised if they were some day told that it was all a 

 delusion, and that Mr. So-and-so had explained the whole thing 

 in a much more simple way. It is to prevent my readers being 

 imposed upon by any such statements or doubts, that I have 

 given this very brief and imperfect outline of the nature, extent, 

 and completeness of the evidence on which the existence of the 

 glacial epoch depends. There is perhaps no great conclusion in 

 any science which rests upon a surer foundation than this ; and 

 if we are to be guided by our reason at all in deducing the un- 

 known from the known, the past from the present, we cannot 

 refuse our assent to the reality of the glacial epoch of the 

 northern hemisphere in all its more important features. 



Effects of the Glacial Epoch on Animal Life : W arm and Cold 

 Periods. — It is hardly necessary to point out what an important 

 effect this great climatal cycle must have had upon all living 

 things. When an icy mantle crept gradually over much of the 

 northern hemisphere till large portions of Europe and North 

 America were reduced to the condition of Greenland now, the 

 greater part of the animal life must have been driven south- 

 ward, causing a struggle for existence which must have led to 

 the extermination of many forms, and the migration of others 



I 



