36 CHAMBERLIN— A POSSIBLE REVERSAL [April i8 



tion of climatic regulation takes on very concrete aspects and pre- 

 sents specific lines of study. 



Subsidiary to these narrow limitations, the recognition of pro- 

 nounced variations is forced upon us by a growing mass of geologic 

 evidence. Throughout most of the well-known geologic periods, the 

 poleward distribution of life implies warm climates, even as high as 

 70° and 80° of latitude. How life of sub-tropical types could have 

 survived the long polar nights is one of the most obdurate puzzles of 

 the earth's climatology. It becomes all the more strenuous if we cast 

 aside all resort to an early fervid state and a molten interior. Quite 

 irrespective of primitive conceptions, however, the edge of the prob- 

 lem has sharpened as we have been forced to recognize that hetzveen 

 the warm polar stages there were episodes of glaciation in strangely 

 low latitudes. It appears necessary now to accept as demonstrative 

 the evidences of extensive glaciation in India, Australia and South 

 Africa in the midst of the later, coal-forming stages of the Paleozoic 

 era. The glacial beds lie even between coal beds of Permian or 

 Permo-Carboniferous age ; while, strangely enough, the areas of 

 glaciation approach and even overlap the tropics of Cancer and Cap- 

 ricorn. And yet, figs and magnolias have grown in Greenland since, 

 and mild polar climates are as well authenticated after as before this 

 climateric glaciation. Less complete evidences from China^ and 

 Norway imply a very much earlier glaciation, falling in the oldest 

 Cambrian or perhaps even pre-Cambrian times. 



The climatic student seems therefore compelled to face oscilla- 

 tions within the known geologic periods ranging from sub-tropical 

 congeniality within the polar circles, on the one hand, to glacial 

 conditions in low^ latitudes, on the other, and these in alternating 

 succession: while neither of these oscillations was permitted to 

 swing across the narrow limital lines of organic endurance. There 

 is little doubt that the ocean, the daughter of the atmosphere, is one 

 of the most potential agencies in controlling these oscillations. It 

 is one of its possible functions in such regulation that invites our 

 present attention. 



Some of the regulating functions of the ocean have long been 



^Willis, "Third Year-Book Carnegie Institution," 1904, p. 282. 



