Therefore, during such frigid times it appears that, with the waters of the Caribbean Sea and Gulf of Mexico reduced to a low temperature, it was impossible for the great Mississippi valley to escape glaciation, while being surrounded by cold seas and glaciated lands which extended even into the tropical latitudes. The broad, level lands of British America and Siberia during the ice age must have been thickly covered by the snow which fell on the deeply frozen plains, besides the large amount of snow that the cold westerly winds must have drifted over their icy surface from lands of greater snow-fall on their western borders. This snow during such freezing times could not be melted away. The great ice-sheets thus formed over wide, level lands could have but little motion in any direction, certainly not sufficient to cause glacial drift of much magnitude; yet the ice-sheet, at one stage of its existence, probably served to widen and deepen the channels of the great rivers which empty into the Arctic Ocean from these vast regions, and the glacial débris from such erosion was deposited in the arctic seas. CHAPTER V. REMARKS ON THEORIES ADVANCED FOR EXPLAINING ICE PERIODS. On Nov. 12, 1891, Professor Geikie made his presidential address before the Edinburgh Geological Society, the subject being “Supposed Causes of the Glacial Period.” Many of his views advanced in this lecture were so much in accordance with my own that I am induced to repeat them. He said that the glacial period was a general phenomenon due to some widely acting cause, and that where we now have the greatest rain-fall the greatest snow-fall took place, and that the Pleistocene period was characterized by great oscillations of climate, extremely cold and very genial conditions alternating. He also said that in glacial and post-glacial times changes in the relative level of the land and sea had taken place, and any suggested explanation which did not fully account for these various climatic and geographical conditions could not be satisfactory. And, while examining the earth-movement hypothesis, he pointed out that in the first place there was not the least evidence of great continental elevations and depressions in the northern hemisphere, such as the hypothesis postulated. Next he showed that, even if the diserrated earth-movements were admitted, they would not account for the phenomena. Such changes, no doubt, would profoundly affect the maritime regions of North America and Europe; but they would not bring about the conditions that obtained at the climax of the ice age.