1895,] Minor Time Divisions of the Ice Age. 239 
altitude and eccentricity being thought perhaps of nearly 
equal influence. The view here presented looks on the Glacial 
period as occurring in a much later time of low eccentricity, 
and for its causation regards altitude as far more efficient than 
any astronomic conditions. The effects of varying astronomic 
conditions have been recently considered by Dr George F. 
Becker, who thinks, altogether differently from Croll, Geikie, 
and Ball, that the combination of minimum eccentricity of 
the earth’s orbit and maximum obliquity of the ecliptic is 
most favorable for snow and ice accumulation; and he states 
that these conditions have existed within the past 40,000 
years, until 8,000 years ago, but he apparently would attribute 
a larger share of the causes of glaciation to geographic con- 
ditions, as land elevation. In Europe a very remarkable 
parallelism of the history of the Ice age with that in America” 
indicates dependence on similar causes, chiefly geographic, as 
epeirogenic movements, with changes of ocean currents, and 
subordinately astronomic. 
If the Glacial period extended through 30,000 or 50,000 
years, depending principally on epeirogenic uplifts and in less 
degree on the cycles of precession of the equinoxes, it would 
agree well with Geikie’s and Chamberlin’s complex history 
of wavering glaciation, and also with its essential geologic 
unity and brevity which have been insisted on by Dana, 
Wright, Hitchcock, Lamplugh, Kendall, Falsan, Holst, 
Nickitin, and other glacialists. To my mind the diversity 
and the unity of this period seem like the opposite gold and 
silver sides of the proverbial shield, concerning which two 
knights, each having seen only one side, valiantly contended. 
Widely extended depression of the ice-burdened land, until 
mostly it had somewhat less altitude than now, initiated the 
comparatively short final epoch of the Glacial period. Tem- 
perate and warm climatic conditions on the ice border, nearly 
as now on the same latitudes, then melted away the ice 
Am. Jour. Sci., IH, vol. xlviii, pp. A Aug., 1893. 
James Geikie, The Great Ice Age, three editions, 1873, 1877, and 1894, 
notably pp. 774, 775, in the third edition ; Journal of Geology, vol. ii, p. 739, 
Oct.-Nov., 1894; Am. Geologist, vol. xv, p. 54, Jan., 1895. 
