CAUSES OF THE GLACIAL PERIOD 577 



winds had free play, and are supposed to have picked up the fine material 

 deposited by the water and to have piled it in great drifts. The chief 

 difficulty with this theory is that we do not now see it in operation ex- 

 cept in a few insignificant cases. There are many places where dry flood- 

 plains are gathering grounds for wind-blown dust, but practically all the 

 cases where this gives rise to loess are in deserts and not at the front of 

 glaciers. 



The cyclonic form of the solar hypothesis seems to afford an adequate 

 explanation of the peculiar phenomena which have just been described. 

 By its very nature the hypothesis demands that belts of excessive stormi- 

 ness and precipitation should lie close to belts of diminished storminess 

 and of aridity. If these did not occur the theory would be untenable. 

 A comparison of figure 20 with figures 11, 12, and 7 shows that in both 

 Europe and America the areas where storminess decreases at times of 

 sun-spot maxima are the areas where loess was abundantly deposited 

 during the Glacial period. Manifestly, if the decrease in storminess 

 which is shown in central Europe and in the central United States in 

 figures 11 and 7 should become intensified, those regions would become 

 deserts and be the sort of places where loess could originate. Just north 

 of the deserts — that is, not far from the ice-sheet — would lie the main 

 track of storms. In summer, when storms were most frequent, their 

 courses would lie farthest north, just as is now the case, and the centers 

 would presumably often pass within the limits of the ice. Therefore in 

 the area fronting the ice the prevailing winds would be from a southerly 

 direction, but ranging well toward both the east and the west. They 

 would be strong winds, for under the assumed conditions of our hy- 

 pothesis the barometric gradients would be steep and the storms would 

 be more severe than at present. The constant indraft of air from the 

 deserts would bring with it great amounts of dust, which would be de- 

 posited in the regions where the glacial streams were depositing their 

 outwash. The net result would be either the accumulation of pure wind- 

 blown loess in areas not subject to inundation by glacial streams, or the 

 deposition of an intermixture of loess and fluvio-glacial materials in the 

 areas where the streams from the ice were laying down their burdens. 

 The agreement of this condition with that which we know to have been 

 the case during the Glacial epoch scarcely needs to be pointed out. 



