J. Croll— Cause of Mild Polar Climates. 27 
and western continents, allowing of a continuous flow of inter- 
tropical water into the Arctic Ocean. Mr. Wallace expresses 
his views on the point thus :—- 
extended across Central Europe between th tic and the 
Black and Caspian Seas, and thence narrower channels south- 
eastward to the valley of the Euphrates and the Persian Gulf, 
the Indian Ocean. From the Caspian also a wide arm of the sea 
extended during some part of the Tertiary epoch northwards to 
the Arctic Ocean; and there is nothing to show that this sea may 
not have been in existence during the whole Tertiary period.’ 
Another channel probably existed over Egypt into the eastern 
basin of the Mediterranean and the Black Sea; while it is proba- 
ble that there was a communication between the Baltic and the 
i islan i 
nel across Afghanistan ma ave opened a 
— the West-Asiatic and Polar seas.”—(‘ Island Life,’ p. 
84, 
My acquaintance with the Tertiary formations of the globe, 
and with the distribution of land and water during that period, 
_ 18 not such as to enable me to form any opinion whatever either 
4s to the probability or to the improbability of the existence o 
such channels as are assumed by Mr. Wallace. But, looking 
at the question from a physical point of view, it seems to me 
pretty evident that if such channels as he supposes existed, 
allowing of a continuous flow of equatorial water into the 
Arctic seas, it would certainly prevent the formation of perma- 
nent ice around the pole, and would doubtless confer on the 
arctic regions a mild and equable climate. This would be 
more particularly the case if, as Mr. Wallace supposes, owing to 
ut at the same time I think it is just as evident that these 
channels would not neutralize the effects resulting from a high 
water flowing into the Arctic Ocean to an extent that would 
Permit of the formation of permanent ice around the pole, but 
