i9o6] OF DEEP-SEA CIRCULATION. 43 



and gvpsiim in not a few periods testify directly to regional aridity. 



The most marked of these are, to be sure, referable to the periods 

 of glaciation, but many of them have no such assignable association. 

 In these periods of warm polar temperature there is reason to 

 believe that the high-latitude temperature-effects fell below the low- 

 latitude concentration-effects and that therefore the deep oceanic 

 circulation was actuated by the dense waters of the evaporating 

 tracts. These may then be supposed to have slowly descended and 

 crept poleward, acquiring a trivial amount of heat from the earth's 

 interior and loosing some to the waters above, but substantially main- 

 taining their temperatures until they rose to the surface in the polar 

 regions and gave their vv-armth to the atmosphere. Aided by the 

 ens-hrouding mantle of vapors that must have arisen from such a 

 body of water, it is conceived that the mild temperatures requisite 

 for the maintenance of the recorded life through the polar nights 

 may have been thus maintained. 



If this be granted, however, it is wise to note that this is not 

 a radical solution of the climatic problem, for a fundamental cause 

 for the conditions that brought on freezing at one period and pre- 

 vented it at others is prerequisite to the postulated influence of these 

 in the reversal of the abysmal circulation. At the best, our sugges- 

 tion offers only an auxiliary agency in the control of secular climates. 

 Some more fundamental agency or agencies must be sought. 



University of Chicago, 

 April i6, 1906. 



