Glacial Theories — Cosmic al and Terrestrial. — Clay pole. 311 
The early speculation of Lyell in the later editions of his 
classic works were marked by the caution so characteristic of 
the man. Attempting to find in changed relations of the land 
and water a sufificient cause for extensive changes in 
-the temperature, and at the same time lacking the 
necessary data in soundings and in geological observa- 
tions outside of Europe he could do little more than 
theorize. And as the progress of discovery showed 
that little solid basis exists at present or had existed in time 
geologically recent for many of his speculative changes, the 
terrestrial theory, as it may be called, gradually lost ground. 
It seemed impossible by means of admissible recent geograph- 
ical movements to find any sufficient cause for so vast a re- 
frigeration as that which the observed phenomena of the Ice 
age appeared to require. Geologists beg?n to look elsewhere 
and to seek in extraterrestrial of cosmical conditions a solu- 
tion of the mystery. Variation of the sun's heat from age to 
age was assigned as a possible means of accounting for con- 
temporaneous variation of the temperature of the earth. But 
no proof or even probability of any such change could be pro- 
duced. The variability of variable stars is in all likelihood 
due to totally different causes. Inequality in the temperature 
of the regions of space through which our system is careering 
is another altogether gratuitous assumption on which a glacial 
theory has been founded. But it is as baseless and as con- 
trary to probability as the former. Moreover, as it has been 
more than once pointed out, either of these two theories 
would have cut ofif the glaciers at their source by reducing 
the evaporation and consequently the rainfall. 
The only cosmical theory that has been rendered sufficient- 
ly plausible to command acceptance is that which was put for- 
ward more than a quarter of a century ago in the pages of the 
"London. Edinburg and Dublin Philosophical Magazine" by 
Dr. James Croll. This, which was in effect terrestrial, though 
based on astronomical facts was supported by its author with 
such ability and ingenuity that it obtained for a time very gen- 
eral approval in the geological world. It not only assigned a 
possible and seemingly a probable cause for the oncoming of 
the Ice age, but required its recurrence at least several times 
during the past, and its repetition on a smaller scale during 
