CHAPTER lY. 



THE SO-CALLED ''GLACIAL EPOCH" AND ITS CLIMATIC CONDITIONS. 



Section I. — Mrodudory . 



Hayixg been led, by a careful consideration of facts observed in many 

 different countries, to the conclusion that a diminution of the earth's mean 

 temperature has been taking place during the successive geological nges, we 

 are now obliged to inquire whether it can be true that at the beginning of a 

 certain epoch — the so-called Glacial — a marked climatic change occurred, 

 a period of much greater cold being suddenly entered upon, which, after 

 lasting for a certain length of time, was succeeded by one of increased 

 warmth, a return to previous conditions taking place after a long interval 

 during wliich a considerably lower temperature had prevailed throughout 

 the earth. That such was the case has undoubtedly, of late years, become 

 the prevalent opinion among geologists, although it is not to be denied that 

 there are some who do not take this view of the climatic conditions requisite 

 ibr bringing about the phenomena of the Glacial epoch. If it be the correct 

 view, and if it can be shown that for the explanation of these phenomena 

 recourse must be had to a general lowering of the earth's temperature, 

 followed bv a change in the opposite direction when the epoch in question 

 came to an end. then it would appear certain that conditions were indicated 

 not at all in harmony with the results supposed to have been reached in the 

 preceding chapter, and we should be obliged to admit that there was some 

 hidden flaw in our chain of reasoning, and that we were mistaken in adopt- 

 ing the view that a gradual refrigeration has been and still is taking j^lace, 

 so that during any previous epoch the mean temperature must have been 

 higher than it now is. Indeed, if it could be proved that the earth is liable 

 to reciu-rent periods of greater heat and cold, the entire course of ottr investi- 

 gations must have been wrongly directed, and all our conclusions would be 

 swept away. 



If, on the other hand, we can show that the phenomena of the Glacial 

 epoch are not necessarily to be accepted as a proof of a generally lower 



