woodworth: geological expeditiox to brazil and chile. 89 



cyclones of the existing atmospheric circulation over the glacial fields. 

 The distribution of land and sea in the Southern Hemisphere was then 

 so different from what it now is, particularly in the Atlantic and 

 Indian regions, that, Avhile we may freely speculate upon a different 

 system of distribution of aqueous vapor, it is at present impossible to 

 construct an unassailable theory. 



The "pendulationstheorie" of H. Simroth (1907) which is but a 

 modification of the iflea of a shifted axis of rotation does not better 

 than the original conception explain the phenomena of distribution 

 of Permian glaciation for the reason that no shifting of polar climates 

 will bring the glacial deposits in the polar regions. Dr. "Wilh. R. 

 Eckardt (1910, p. 125-127) has well observed in connection with the 

 above mechanical hypothesis that Sumatra, assumed to be one of the 

 fixed equatorial poles of pendulation in this speculation, is placed on 

 the borders of the principal area of Permian glaciation and hence no 

 essential shift is accomplished. 



The recently elaborated hypothesis that glaciation may be brought 

 about through the temporary reduction of the amount of carbon in 

 the earth's atmosphere appears to fail as an adequate explanation of 

 the phenomena of glacial periods since the view does not explain the 

 succession of epochs of glaciation and deglaciation in the Pleistocene 

 period. Four times in this period the ice-sheets apparently came on 

 and went oflf. If the abstraction of carbon in the form of coal and 

 limestones in the preglacial period led to the first ice accumulation 

 and advance, the h\pothesis leaves unexplained the shortly succeeding 

 ice advances between whose dates no corresponding appreciable 

 reduction in the carbon is registered by rock-making in the earth's 

 crust. 



As we do not know with any certainty the cause of the latest glacial 

 periods so near our own times, it is Evident that the geographical 

 conditions of the Permian must be thoroughly ascertained before we 

 can construct a plausible explanation of a glacial period so remote and 

 taking place on lands whose contours are as yet drawn with too much 

 conjecture. Certain lights appear however to be burning as guides 

 to the path which shall lead to the discovery of the probable cause of 

 Permian glaciation. These may be briefly summarized as follows: — 

 The axis of the earth appears to have lain in Permian times where 

 it does now. This excludes a favorite group of hypotheses. 



The glaciated lands of south Brazil and German southwest Africa 

 were in Permian time at or near sea-level. This does not exclude the 

 extrusion of glaciers from highlands to the sea-border provided the 

 highlands lav over the site of the Atlantic basin. 



