CLIMATE AND CARBONIC ACID. 255 



its pole at a point located somewhere north of Hudson Bay. One effect 

 of this oblique rotation is to establish in northern latitudes between 50 

 and GO degrees two areas of low barometer and one of high barometer, 

 a disposition which is in strong contrast to the condition in the south- 

 ern hemisphere, there being a zone of high pressure along the parallel 

 of 35 degrees, south latitude, with decreasing pressure thence toward 

 the Antarctic. These lows and highs differ from those which are 

 familiar as features of daily weather maps, in that they are nearly sta- 

 tionary. The well-kno^vn migrant centers converge toward and run 

 into the great fixed centers. The two permanent lows are situated 

 one across the North Atlantic, from Hudson Bay to Scandinavia, the 

 other in the North Pacific, from Japan to southern Alaska. They are 

 centers of inflowing ascending air currents, and are, therefore, char- 

 acterized by great precipitation. The region of maximum glaciation 

 at the present time lies between them; one conspicuous development 

 occurring in Greenland in the northwest quarter of the Atlantic low, 

 another lying in Alaska in the northeast quarter of the Pacific low. 

 By an analysis of the winds, it is shown that both Greenland and 

 Alaska lie to leeward of the prevailing currents wl^ere they pass ashore. 

 They are not necessarily the provinces of maximum precipitation, rain 

 and snow both considered, but they are areas of copious snowfall, with 

 low annual mean temperatures. 



The northern high lies nearly midway between the two lows over 

 Siberia. In contrast to them, it is a center of descending outward- 

 flowing currents, marked by slight precipitation, and it is not now, nor 

 was it in Pleistocene time, a scene of glacial development. 



The centers of Pleistocene glaciation were so arranged with refer- 

 ence to the glacial regions of to-day that they would be determined by 

 the oblique circulation and distribution of areas of low pressure, if 

 existing conditions were intensified. An adequate occasion of intensifi- 

 cation is found in the thermal transparency of the atmosphere, resulting 

 from depletion of carbon dioxide, and thus the localization of Pleisto- 

 cene ice sheets is explained in a manner consistent with the major 

 hypothesis of the cause of glaciation. 



Chamberlin's hypothesis is framed on an atmospheric basis, but the 

 efficiency of the agencies which it postulates depends upon geographic 

 conditions, upon distribution of land and sea and average heights of 

 continents. The geography of the earth in the closing epochs of the 

 Paleozoic era is known only in its broadest outlines, and they are but 

 vaguely traced. With such imperfect data it is impracticable to explain 

 satisfactorily the extraordinary phenomena of glaciation at that date 

 in intimate association with the development of coal beds and extend- 

 ing within the tropics. Nevertheless, to carry out his purpose of 

 developing a working hypothesis, the author feels obliged to arrange 



