That evaporation was an especially important factor in causing the ice from the Keewatin center to disappear, is suggested by the relatively small amount of water-sorted material in its drift. In South Dakota, for example, less than 10 per cent of the drift is stratified.[45] On the other hand, Salisbury estimates that perhaps a third of the Labradorean drift in eastern Wisconsin is crudely stratified, about half of that in New Jersey, and more than half of the drift in western Europe.
When the sun's activity began to diminish, all these conditions, as well as several others, would coöperate to cause the ice sheets to disappear. Step by step with their disappearance, the amelioration of the climate would progress so long as the period of solar inactivity continued and storms were rare. If the inactivity continued long enough, it would result in a fairly mild climate in high latitudes, though so long as the continents were emergent this mildness would not be of the extreme type. The inauguration of another cycle of increased disturbance of the sun, with a marked increase in storminess, would inaugurate another glacial epoch. Thus a succession of glacial and inter-glacial epochs might continue so long as the sun was repeatedly disturbed.
[Footnote 38: This chapter is an amplification and revision of the sketch of the glacial period contained in The Solar Hypothesis of Climatic Changes; Bull. Geol. Soc. Am., Vol. 25, 1914.]
[Footnote 39: R. D. Salisbury: Physical Geography of the Pleistocene, in Outlines of Geologic History, by Willis, Salisbury, and others, 1910, p. 265.]
[Footnote 40: The Quaternary Ice Age, 1914, p. 364.]
[Footnote B: For fuller discussion of climatic controls see S. S. Visher: Seventy Laws of Climate, Annals Assoc. Am. Geographers, 1922.]
[Footnote 41: Many of these alterations are implied or discussed in the following papers:
1. F. W. Harmer: Influence of Winds upon the Climate of the Pleistocene; Quart. Jour. Geol. Soc., Vol. 57, 1901, p. 405.
2. C. E. P. Brooks: Meteorological Conditions of an Ice Sheet; Quart. Jour. Royal Meteorol. Soc., Vol. 40, 1914, pp. 53-70, and The Evolution of Climate in Northwest Europe; _op. cit._, Vol. 47, 1921, pp. 173-194.