AVPRODHMESIS OF CAUSE OF GLACIAL PERIODS. 773 
fundamental postulates of the atmospheric hypothesis as are 
needful to give an atmosphere compatible with glaciation under 
such other conditions as prevailed in India, Australia and South 
Africa in the later Paleozoic. . 
2. The localization was most extraordinary. The chief areas 
lay under the tropics —the Indian, under the Tropic of Cancer 
and the Australian and South African, under the Tropic of Cap- 
tricorn. The Indian area stretched southward to 17° 20’ N. Lat. 
and northward to the vicinity of 35°. The Australian area 
stretched north to 20° 30’ S. Lat. and southward (in Tasmania) 
to 42°. The extent of the South African area is less well known, 
but centers about 30° S. Lat. It appears then that on both 
sides of the equator glaciation reached two or three degrees 
within the tropics, while in the opposite direction general glacia- 
tion has not been traced beyond 42° To the south this signifies 
little because of the prevalence of the sea. To the north the 
apparent limitation is very singular and doubtless very signifi- 
cant. It cannot, however, be positively asserted that glaciation 
did not prevail in the higher latitudes, but no decisive evidence 
of it has yet been discovered. At the same time it must be 
recognized that many evidences of remarkable transportation 
and of unusual bowlder accumulation, and indeed of occasional 
striation have been reported, and that these have been attributed 
to glacial agencies by geologists of high standing. It cannot be 
affirmed at present that these phenomena were precisely con- 
temporaneous with the glacial deposits of the oriental tropics, 
but they were nearly so. 
In the southern portion of Brazil there are deposits strikingly 
similar to the glacial beds of Africa and Australia, but no stria- 
tion or distinctive marks of glaciation have yet been authorita- 
tively reported. 
The southernmost extent of the lowland Pleistocene glacia- 
tion was about 37° N. Lat. The Paleozoic glaciation, therefore, 
reached 20° farther. 
The altitude of the glaciation.—Respecting the altitude at 
which the Paleozoic glaciation took place, it is to be remarked 
