PERMO-CARBONIFEROUS GLACIAL DEPOSITS ROR 
of Parana,’ we may conclude that the region was at that time not a 
tableland but a comparatively low plain. In any case the whole 
character of the widespread, almost flat sheet of tillite in southern 
Brazil is such as must have resulted from ice action of the conti- 
nental type. Mountain glaciers could not have provided so 
extensive, uniform, and relatively horizontal a deposit as the 
Brazilian geologists have found. 
From what center the ice spread out is not known, though the 
numerous bowlders of granite and gneiss suggest a motion inland 
from the belt of Archean along the Atlantic coast. In that case the 
ice-sheet must have extended far toward the southeast, perhaps 
beyond the present’edge of the continent. However, there are 
granites and gneisses farther west, and outcrops of these rocks 
which existed in Carboniferous times may lie buried under later 
deposits toward the west or north. The bowlders of ancient 
conglomerate containing jasper may some day be traced to their 
source, giving evidence of the direction in which the ice moved. 
As to the tillites of the Rio Sauce Grande and of the belt along 
the foothills of the Andes near San Juan, the areas known to be 
covered by them are so small that local mountain glaciation might 
perhaps account for them; though the fact that tillite of the same 
age occurs on the Falkland Islands and that a great ice-sheet 
covering many thousands of square miles reached sea-level a few 
hundred miles to the north or east suggests that a very large part 
of South America must have been ice covered. It is not unlikely 
that the areas of ice action coalesced to form a single great sheet 
T,300 miles or more in diameter and covering hundreds of thousands 
of square miles, something comparable to the vast continental ice- 
sheets of Europe or North America in the Pleistocene. The 
northern edge of this ice-sheet reached at least one degree into the 
tropics in Brazil; and this occurred, not on high mountains, but on 
comparatively low ground, as shown on a former page. 
Recent advances in the study of the South American Permo- 
Carboniferous glacial deposits bring that continent into the same 
rank as South Africa and Australia with respect to the area then 
covered by ice, while India has been much surpassed. The mag- 
nitude of the geological problem involved is growing from year to 
* Woodworth’s Report, p. 20. 
