676 GEOLOGY. 



nection from India, via Australia and the old submerged land, to New Zealand, 

 and thence to Antarctica, and through this to South America. Other and more 

 northerly connections between India and South Africa, and between the latter 

 and South America, have usually been postulated. In the minimum case, 

 the oceanic circulation must have been very different from the present, for the 

 warm equatorial currents from the Pacific that now flow through the East Indian 

 straits into the Indian Ocean must have been turned back into the Pacific, con- 

 centrating its heat there. At the same time, two thirds of the cold waters flowing 

 along the borders of Antarctica, which now largely pass south of New Zealand 

 into the Southern Pacific, must have been arrested by the postulated New Zea- 

 land- Antarctican isthmus and turned northward into the Indian Ocean. The 

 joint result was a concentration of warm water in the Pacific, and of cold water 

 in the Indian Ocean. 



A broad Arctic tongue of sea is thought to have occupied eastern Russia and 

 western Turkestan about this time. It appears to have had an open polar mouth, 

 but its ulterior connections in the Arctic regions are unknown. So, too, its con- 

 nections toward the south and east are uncertain at the precise time of the gla- 

 ciation. It is not, however, beyond permissible hypothesis to suppose that 

 this Arctic embayment may have been occupied by a returning Arctic current 

 of the Labrador type. If so, this tended to extend the Arctic low temperature 

 equatorward in about the same longitude as the Antarctic movement. 



The hypothetical development of localized glacial conditions. — The postulated 

 effect of these configurations was the concentration of large portions of 

 the polar currents in the longitude of the glacial areas, resulting in the intensi- 

 fication of the atmospheric gradients on that side of the sphere, and leading to 

 a peculiar asymmetry in the atmospheric circulation. Hypothetically, this 

 called into play, in an unusual degree, the derivative mechanical factors in the 

 circulation, and led to the development of fixed cyclonic areas in exceptionally 

 low latitudes. The cold polar currents are assumed to have furnished to the 

 centers of the fixed "lows, " cool moist air, which, forced to rise rather by mechan- 

 ical movement and aqueous kinetic action than by high temperature, gave per- 

 sistent precipitation at sufficiently low temperatures to promote glaciation. Per- 

 sistent clouds and fogs, habitual in such situations, are presumed to have shielded 

 the glacial surface by their high reflecting powers, and to have become 

 important auxiliary agencies. 



Alternative views. — The special problem of Permian glaciation has not 

 developed such voluminous discussion as has that of the Pleistocene period, 

 largely because its verity has only recently been established, and because the 

 majority of glacial students are not personally familiar with its phenomena. 

 A change of the earth's poles has naturally been suggested, since a shifting of 

 the south pole to the center of the Indian Ocean would relieve the problem of 

 its most refractory element, the location of the glacial areas on the borders of 

 the tropical zone. Such a shifting, even if we ignore the extremely serious dy- 

 namical difficulties involved, does little more than mitigate the problem of locali- 

 zation, for if the pole were placed equidistant from the three glacial centers in 



