o6-i r. H. KXOWLTOX EVOLUTIOX OF GEOLOGIC CLIMATES 



cloud mantle through the winter over such high latitudes resulting from the 

 air being colder than the water."' 



Barrell also tliinks that the problem is made easier of solution if there 

 can be found evidence of the truth of the reversal of deep oceanic circu- 

 lation, but cert-ain of the facts that seem to offer a fatal objection to this 

 yiew have already been presented (page 559). 



To return for a moment to the views expressed by Barrell : It is easy 

 to believe that with a low land-mass and broad, shallow, epicontinental 

 seas the temperature would be somewhat raised, thus inducing greater 

 evaporation, greater cloud formation and rainfall, and in the end a 

 milder, more equable climate : but it seems to me difficult to believe that 

 this would be of sufficient importance and magnitude to account for the 

 varied phenomena that must be explained, especially as it appears to be 

 predicated on the currently accepted theory of solar control of earth tem- 

 peratures. The equable moist climates of the regions cited, Ireland and 

 Patagonia, must in part be due to topographic conditions and in part to 

 ocean currents, and any attempt at a poleward extension of these condi- 

 tions to cover the 30 degrees between these localities and the poles would 

 seem to present insuperable difficulties, especially when we consider the 

 vast eons of time that must be accounted for in the ages before the Pleis- 

 tocene. Therefore, it seems to me highly improbable that the factors 

 called into play could have been of sufficient magnitude to have caused 

 and maintained polar geniality, such as happened again and again. Still 

 less does it seem that they could account for seaJeveJ glaciation in middle 

 and equatorial latitudes such as that of the "Permo-Carboniferous."' 



Summary axd Coxclustoxs 



Xow we have come to the point where it is proper to ask what progress, 

 if any. we can presume to have made toward a solution of the several 

 problems connected with the study of geologic climates. The various 

 h}'potheses and theories have been passed in a more or less critical review, 

 and it is believed that a certain amount of chaff has been cleared away, 

 thus laying a possible foundation for an acceptable explanation: but 

 probably it would be altogether too much to claim that any hypothesis 

 has been so far advanced that it is likely to receive universal acceptance. 

 Barrell, when confronted by a somewhat similar interrogation, states 

 flatly that ^*the depths of geologic time leave us face to face with the 

 unknown.'"' 



To my mind, however, the case does not seem quite so hopeless. The 

 facts that have been presented regarding the warm oceans of much if not 



