THE ICE AGE. CLIMATE AND TIME. 
235 
It is essential to the understanding of the theory deal- 
ing with those vast climatic changes, which the science of 
geology teaches ns to believe it has discovered, by its inductive 
process of examining the organic remains preserved in, and the 
physical phenomena engraved on, our rocks, that the evidences 
collected should be succinctly given. 
The evidences of predominance of a high temperature over 
a defined period, or within a well marked region, will be found 
preserved in the character of the flora and the fauna , which 
existed when the strata, in which their forms are fossilised, was 
in the progress of consolidation. As tropical life now differs 
from that which exists within the arctic circle, so through all 
time similar differences in organisation have been produced by 
the influences of a high temperature or a low one. We dismiss 
from consideration in this paper any influence which may be 
supposed to be due to purely terrestrial heat ; the agencies 
with which we have to deal being sufficiently powerful to over- 
come, and, as it were, to mask the effects due, if any, to 
subterranean temperature. The palaeontological evidences are 
numerous and decisive upon the question of the alternations of 
climate which have taken place in those long lapses of time, 
during which the surface of our planet has been slowly under- 
going those changes, which have . produced that succession of 
stratified rocks, which is the great stone book of Nature, bear- 
ing engraved in forcible language, the history of her grand 
mutations. With those we have only incidentally to deal until 
we arrive at the Post-tertiary period, when we glean, from the 
evidences of some great mechanical force which has left its 
markings, a knowledge of the fact that there ensued a period 
of great cold, which covered Northern Europe and our own 
islands with masses of moving ice. 
It should be remembered that there can be no doubt but 
that several long epochs of great cold existed before that period, 
which is more especially to engage our attention. The fossil 
remains from which the geologist forms his estimate of the 
character of a climate during any geological period, are 
abundant during the epochs which may be distinguished as 
warm or tropical ; but as a general rule those formations which 
geologists are inclined to believe indicate a cold condition of 
climate, are nearly devoid of fossil remains. The secular changes 
of climate which will be more especially noticed as occurring 
during, and since, the Great Ice Age, were the result of certain 
physical causes, recurring in obedience to fixed laws, which 
must have taken place during those vast periods of time which 
are lost in the infinite past. 
Let us now examine — though the examination must neces- 
sarily be brief — some of the phenomena presented by existing 
