28 J. Croll— Cause of Mild Polar Climates. 
it certainly would greatly diminish the flow into the Arctic 
Ocean. Supposing that at the commencement of the last Glacial 
epoch the volume of the Gulf-stream to have been dou 
what it is at present; this condition of things would not have 
prevented the operation of these physical agents which brought 
about the Glacial epoch, although it, no doubt, would have 
considerably modified the severity of the glaciation resulting 
from their operation. The very same thing would hold true, 
though perhaps in a much greater degree in reference to the 
channels assumed by Mr. Wallace. 
If the emissive power of the sun was about the same during 
the Tertiary period as at present, and there is no good grounds 
for supposing it was otherwise, then the extra heat possessed by 
the northern temperate and arctic regions must have been 
derived either from the equatorial regions or from the southern 
hemisphere, or, what is more likely, from both. If so, then 
the temperature either of the southern hemisphere or of the 
intertropical regions, or both, must have been during the Ter- 
tiary period much lower than at the present day. A lowering 
of the temperature of the equatorial regions, resulting from this 
transference of heat, would tend to produce a more equable 
und uniform condition of climate over the whole of the north- 
ern hemisphere. As the area of the Arctic Ocean is small in 
