HYPOTHESIS OF CAUSE OF GLACIAL PERIODS 785 
lands and South America, the ocean currents may be pictured as 
sweeping eastward from South America along the icy borders of 
the Antarctic continent into the great bay south of Australia, out 
of which they recurved and flowed northward across the equator 
to the Indian peninsula, which they freely bathed, and, returning 
along the supposed Gondwana connection, wrapped about South 
Africa and then flowed northward toward the equatorial regions, 
a portion then curving backwards and descending the coast of 
South America to complete the circuit. Such a circulation would 
throw perhaps two thirds of the antarctic influence into the 
Indian Ocean. On the other hand, seven eighths or more of 
the equatorial influence would probably be brought to bear 
upon the Atlantic and Pacific oceans. Asa result these oceans, 
notwithstanding the impoverished condition of the atmos- 
phere, received and retained a large percentage of the sun’s 
heat. 
Referring to the principles stated earlier in this discussion, 
it may be remembered that it was noted that a diathermous 
atmosphere permits a larger part of the sun’s heat to reach the 
surface of the earth than a thermally opaque atmosphere, and 
that the portion which falls upon the ocean for the most part 
penetrates it until it is absorbed. A certain part, to be sure, is 
reflected, but in the zone of nearly vertical rays this is reduced 
to the minimum. As the result of the ocean’s ability to absorb 
and retain heat, the diathermacy of the atmosphere is of less 
consequence in equatorial oceanic regions than in land tracts and 
hence the great equatorial oceans may have remained measurably 
warm throughout the glacial period. 
It is conceived, therefore, that under these conditions, glaci- 
ation may have been produced in exceptionally low latitudes, and 
that its distribution was closely associated with the Indian Ocean. 
At the same time it is conceived that the lands immediately 
adjacent to the Atlantic and Pacific oceans, especially in low 
latitudes, were so far affected by the favorable thermal condition 
of those great bodies as to enjoy relatively mild temperatures, 
at least temperatures sufficiently genial to save them and the 
