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 upwards 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 : Warm 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 
