Earth's Earhj Hisiorij. 319 



The Permo-Carboniferous giaciation was so much 

 longer and more severe than that of the Pleistocene that 

 all the clmiatic features of the latest glacial time must be 

 assumed to have been far surpassed in intensity in the 

 late Paleozoic. The supposed mantle of clouds and the 

 warm earth beneath completely disappear, and with them 

 departs the 'N'ebular theory, unless the whole process of 

 cooling was complete before the end of the Carboniferous. 



As one goes backward in geological time the evidence 

 for ice ages naturally grows more fragmentary ; but the 

 proofs of a late pre-Cambrian or early Cambrian glacial 

 period affecting large parts of Australia and South 

 Africa, and touching also Europe, Asia, and North 

 America, seem sufficient to infer conditions more severe 

 than those of the Pleistocene. The Lower Huronian ice 

 age, shown certainly and widely in northern Ontario, may 

 have had a much greater extension, reaching the United 

 States, Finland and India ; and there are still older bowl- 

 der conglomerates, in the Timiskaming, Dore and Seine 

 Series of North America, and in Finland, that suggest ice 

 action, though the tinal proofs of ice work, such as 

 striated stones, etc., have not yet been found because of 

 the mountain-building changes these rocks have under- 

 gone. 



As suggested bv the present w^riter in a presidential ad- 

 dress on '^Dry Land in Geology'' (G. S. A., 1916), there 

 is no convincing evidence afforded by Geology to show 

 that the earth was ever hot. The earliest 'known rocks 

 were water formed, proving a temperature not higher 

 than the boiling point at the very beginning of the acces- 

 sible record of Geology ; and the next later formations in- 

 clude rocks formed under the influence of seasonal 

 changes and of ice sheets. 



The usually genial earth, clothed during much of its 

 later history with rich forests, even to the poles, has under- 

 gone crises of severe climate from time to time since the 

 beginning. These short periods of stress have probably 

 been more effective in the rapid development of the 

 world's inhabitants than all the long, warm and hazy 

 periods which intervened. 



University of Toronto. 



