3\>R>ence0 of an flee B0e, 213 



But there are later investigators who make the 

 time much shorter, not over 10,000 years. 



So much for the time; but you ask What 

 about the occasion, or cause ? This is a ques- 

 tion that many have attempted to answer, 

 there having been eight or ten theories pro- 

 mulgated with regard to the cause of the gla- 

 cial period, but no one of them is entirely 

 satisfactory, and only two or three of them are 

 deserving of much discussion. It is always 

 interesting to know what people think, how- 

 ever, even if we do not agree with them. 



The first theory named is that the glacial 

 period is due to the decrease of the original 

 heat in our climate. This theory can be dis- 

 missed by saying that the planet was cooling 

 at the time and has been cooling ever since, 

 and that the reasons for an ice age are greater 

 now than then, on that theory. Another 

 theory assumes that at some former period 

 there was a greater amount of moisture in the 

 atmosphere ; while this of course would be the 

 occasion for greater precipitation of snow, it 

 does not account for the changing conditions 

 that would produce the ice effect. That there 

 was a preglacial period there is abundant evi- 

 dence, in buried forests, the filling up and 

 changing of river beds, and other evidences 

 that will be referred to further on. This 

 theory, unmodified and stated broadly, is not 

 satisfactory. Another way of accounting for 



