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Page:Popular Science Monthly Volume 44.djvu/835

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THE GLACIAL PERIOD EAST AND WEST.

5. As the above review of facts makes manifest, the division among geologists on the question, and the differences in intensity of opinion, are to a large extent geographical.

The cause of this sectional divergence in views deserves consideration. The writer has come to the conclusion that the cause is largely meteorological: that the geological differences in opinion are a consequence not only of differences in observed facts in the West as compared with those of the East, but back of these, in meteorological differences in the two regions during the Glacial period.

At the present time the glaciated areas of eastern and central North America differ widely in hygrometric conditions. For New England and three fourths of the State of New York the mean annual precipitation, according to Schott's maps, varies from thirty-eight to forty-two inches—a broad coast region, nearly half the breadth of New England, excepted over which it amounts in some parts to fifty inches; while for Wisconsin it varies from thirty-two to thirty-eight inches, and for the larger part of Minnesota, from twenty to thirty-two inches. North of New England, in British America east of Hudson Bay, the annual precipitation is from thirty-two to twenty inches; but to the west of this region, over Manitoba and beyond, it is twenty to ten inches.

Here is a large present difference between the eastern and western regions, affecting snowfalls as well as rainfalls.

Now, in the Glacial period, this eastern region would not only have had the same great advantage as now of proximity to the Atlantic Ocean, but also that of greater height than now. The evidence appears to be conclusive that along the Atlantic side of the continent from southern New England northward, as well as on the Pacific side, the continent stood much above its present level, and that the elevation was the culmination of that which was in progress during the closing part of the Tertiary era—as urged by Prof. Upham. However much the surface of the great medial valley of the continent was raised, it can not be reasonably questioned that the border mountain regions experienced the greater amount of elevation. Hence, with the mountain condensers on the east so much increased in altitude and extent, the differences between the eastern and interior regions as to precipitation would have been greatly augmented, to the advantage of the eastern region.

Further, the Glacial period was probably a time of greater precipitation than now, as well as of greater cold. Some have said, of greater precipitation, and not of greater cold; but the former of these two statements has general acceptance. If the surface waters of the Atlantic basin were warmer than now—owing to a rise of land along a belt from southeast to northwest through