370 PAST succession: the ceneosere. 



less extent in Etirope, the more equatorial of the two belts of storms would 

 keep the air of the torrid zone in active motion. Tropical hurricanes would 

 be more numerous than now, and storms of the eastward-moving type, char- 

 acteristic of the temperate zone, would aboimd somewhat to the north of 

 the region of hurricanes. The active upward movement of the air in the 

 storm centers would produce an abundance of rain and would carry away an 

 abundance of heat. New air would be continually brought from the lands 

 to the oceans and back again, so that evaporation would increase, even 

 though the temperature were lower than now. Thus two conditions would 

 tend to promote the accumulation of snow and the formation of glaciers 

 among the mountains. In the first place there would be more precipitation 

 than now, and in the second place there would be less melting. Such condi- 

 tions would prevail as far north as the center of the subtropical storm belt. 

 Beyond this would lie the median belt of decreased storminess. The tempera- 

 ture there would apparently be lower than now, but the degree of lowering 

 would presumably not be so great as within the tropics. Storms would occur 

 in summer when the subtropical storm belt moved north, and in winter when 

 the boreal belt moved south. Yet the actual amoimt of precipitation would 

 probably, and indeed almost certainly, be less than at present. 



"North of the subarid zone would lie the great boreal storm belt. Farther 

 north than now and more intense it would whirl its storms around the edge 

 of the highlands of Labrador and Scandinavia. It would not only cause pre- 

 cipitation, but also constant cloudiaess. Thus the snows of winter would 

 have scant chance to melt. In the colder districts they would gradually 

 accumulate, and as the storms grew more numerous great areas of permanent 

 snow would apipear, and continental glaciers would at length begin to creep 

 forth. In their cold centers areas of high pressure woidd doubtless exist 

 like those which now prevail in Antarctica and Greenland. The presence of 

 these centers would in itself increase the severity of the winds, for it would 

 establish high barometric gradients, down which the winds would sweep 

 viciously. The growth of the glacial area would cause the region of high 

 pressure also to increase in size, and thus the boreal storm belt would be 

 pushed equatorward and would maintain its position along the ice-front. As 

 long as the sun maintained its high degree of activity the storms would con- 

 tinue and the glaciers would grow. Then when the solar disturbances ceased 

 the terrestrial storms would also decrease in severity, the two cyclonic belts 

 of each hemisphere would tend to merge, precipitation and cloudiness would 

 decrease, and the sun would have an opportunity to melt the accumulated 

 ice" (573-574). 



"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 storminess 

 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 

 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 Evu-ope and in the central United States 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 he the main track of storms. In smnmer, when storms 

 were most frequent, their courses would lie farthest north, just as is now the 

 case, and the centers would presiunably often pass within the limits of the 

 ice. Therefore in the area fronting the ice the prevailing winds would be 



