242 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1924 



earth is less heated by the radiation from the sun than if mountain- 

 making had not happened. 



The carbonic acid hypothesis (Arrhenius) will here come under 

 consideration. But an examination will show that no such diminu- 

 tion in the supply of carbonic acid as the theory requires to explain 

 the severer climate — i. e., lessening of volcanic activity — happened 

 in the miothermic ages. On the contrary, volcanism was most power- 

 ful during the orogenic phases and immediately after them, while 

 again, it was least active during the anorogenic and pliothermic 

 periods. Thus, even for these reasons alone the carbonic acid 

 theory is not applicable. 



The simplest and most probable interpretation of the connection 

 between orogeny and climate lies herein, that the orocratic relief 

 which the continents had after an orogenic phase, influenced the 

 climate in such a manner as to establish miothermic conditions. 

 Wlien, again, the continents were pediocratic, as in anorogenic times, 

 the climate became pliothermic. 



It is well loiown that a climate is modified by the relief and the 

 elevation of a region, and that with increasing altitude it gradually 

 becomes cooler and even glacial. Further, mountains and high- 

 lands exercise a great effect as condensers of precipitation, as bound- 

 aries of climate, etc. But meteorologists and geologists reflect less 

 often that the relief of the continents influences not only the local 

 or regional climate, but the whole economy of the calories which the 

 sun supplies. In the paper cited, " Orogenesis und Klima," I have 

 endeavored to show that the influence of relief on the climate can 

 be remarked in the following circumstances. 



1. The more the radiation from the earth can be retarded, the 

 more the temperature rises. In this storing of heat the atmosphere 

 plays the chief part by its selective absorption, the effect of which 

 has been compared with that of the glass on the hotbed. It yields 

 the most favorable result on extensive lowlands, and if all continents 

 were pediocratic, as supposed for pliothermic periods, they would 

 profit by the sun's heat at the highest temperature. But this so-to- 

 say ideal thermical state is disturbed by an orocratic relief. The 

 air mantle upon the mountains and highlands is thinner and less 

 dense than the atmosphere over the lowlands. In consequence, 

 insolation certainly is greater, but the loss of heat by radiation into 

 space has increased in a much higher degree. Moreover, as in all 

 mountain regions the rising of warm and sinking of cold air are en- 

 hanced by the greater insolation and radiation, the loss will thus 

 be accelerated. In the above comparison with the glass on the hot- 

 bed, the lofty parts of the continents can be regarded as holes in 

 the glass. They not only chill the place just beneath them, but more 

 or less the whole hotbed. 



