EFFECT OF CLIMATIC CHANGES ON GLACIATION 565 



formed unless the water had stood at approximately the same level for 

 centuries. In the second place, the strands of the Dead Sea, to take the 

 most striking example, could not possibly have been produced in this way, 

 because the surrounding mountains do not rise high enough. No signs 

 of glaciation have been described in any. part of the area draining to that 

 lake. Slight moraines are found on the west side of the Lebanon Moun- 

 tains, but no part of this range drains to the Jordan Eiver. There is no 

 reason to think that there was any great accumulation of permanent snow, 

 even at the height of the Glacial period, for no part of the drainage basin 

 of the Jordan except the very top of Mount Hermon rises high enougli. 

 Even there the possible snow-covered area is not a tenth the size of the 

 Dead Sea. The only feasible explanation of the strands of the Dead Sea 

 seems to be changes of climate which express themselves chiefly in vari- 

 ations in the amount of precipitation. This conclusion applies to many 

 other lakes, both in the Old World and the New. 



The Causes of the Glacial Period 

 general discussion 



We have now examined the little climatic changes which occur within 

 the limits of the 11-year sun-spot cycle, the greater changes of historic 

 times, and the still greater changes of the period between the culmina- 

 tion of the last Ice Age and the beginnings of history. We have seen that 

 they all appear to be of the same type, although differing in degree, and 

 that all are apparently explicable on the hypothesis of a shifting of cli- 

 matic zones, such as now occurs on a small scale with each increase and 

 decrease of sun-spots. This brings us face to face with the Glacial 

 period. We must now examine, that in respect to the three possible 

 hypotheses of crustal deformation, chaiige in the amount of GOo, and 

 changes in the activity of the sun's surface. No serious student of geology 

 would question that the deformation of the earth's crust and the resultant 

 upheaval of mountains, elevation of continents, and formation of barriers 

 in the ocean must have had most pronounced and long-continued effects 

 on the climate. Such deformation must be regarded as one of the pri- 

 mary climatic factors. In the production of Glacial stages and epochs 

 as distinguished from Glacial periods, however, there is little ground for 

 the idea that it has been the chief factor, or even a factor of great impor- 

 tance. That the earth should have heaved up and down sufficiently to 

 cause such vicissitudes, and yet that the evidence of it should be so weak 

 and in many cases so strongly contradictory, is scarcely probable. A few 

 geologists, to be sure, still cling to the idea tliat glaciation was due to an 

 upheaval of the lands. They are forced, however, to reject most of the 



