CLIMATE AND TERRESTRIAL DEPOSITS 189 



FOR ARID CLIMATES 



1. Warm-temperate arid: moderate sun and wind action. 



2. Tropical arid: strong sun and wind action. 



3. Cold-temperate arid : strong frost and wind action. 



FOR RAINY CLIMATES 



1. Temperate rainy: moderate mechanical and chemical disinte- 

 gration. 



2. Tropical rainy: moderate mechanical, intense chemical dis- 

 integration. 



3. Subpolar rainy: intense mechanical, moderate chemical dis- 

 integration. 



The evidence in regard to the relative position of the varieties 

 of rainy climate does not seem to be as secure as that in regard to the 

 arid climates. 



In comparing the rainy climates to the arid it is thought that, on 

 the whole, the rainy climates are the greater destroying agents, but 

 so many factors enter in the final result that it is thought that a change 

 toward semiaridity will hasten instead 0} retard erosion through a 

 weakening of the vegetal covering and a concentration of rainfall. 

 The local accumulations of waste resulting from a movement toward 

 aridity, while apparently indicative of great erosion, should really 

 from their mere presence not be allowed to influence the judgment. 



Recent geological times have been marked by climatic oscillations 

 of great magnitude resulting in synchronous erosional and sedimentary 

 oscillations. In past geological times other climatic oscillations 

 must be presumed to have taken place frequently, though normally 

 of much less intensity than during the past ice age. The sedimentary 

 effect of climatic variations as well as stable climates is therefore of 

 geological importance. From the previous discussion it would appear 

 that any variation from a temperate climate, either arid or pluvial, 

 would involve a temporary, abnormally rapid increase of rock waste 

 until the regolith had become adjusted to the new conditions. Any 

 variation toward these temperate means, such as the normal changes 

 in the temperate zones since glacial times, will result, on the other 

 hand, in a rapid slackening of rock destruction. Through geological 

 time, therefore, the slowly but perpetually fluxing climates would 



