Causes and Conditions of GlaciatiQn. — tTpham. 17 
Wright's "Ice Age in North America" (pp. 435, 592), is in- 
consistent with Falsan's and Manson's views, which have no 
place for general glaciation before the Pleistocene period. 
Another obstacle to Manson's hypothesis of a continuous cloud 
envelope till after the Quaternary glaciation consists in the 
extensive deposits of rock salt and gypsum found in strata 
as old as the Silurian and Cambrian, since these beds could 
only be formed by evaporation of lagoons shut off from the 
sea, or of saline lakes, under a drying atmosphere. 
The epeirogenic theory of glaciation, thought out by Dana, 
Le Conte, Wright, and other American glacialists, and by 
Jamieson in Scotland, which has been presented in the Am. 
Geologist (vol. vi, pp. 327-339, Dec, 1890; vol. xin, p. 278, 
April, 1894), in "The Ice Age in North America" (pp. 573- 
595). and the American Journal of Science (vol. xi.vi. pp. 
114-121, Aug., 1893), is held by Falsan to account for the 
Glacial period, but it is rejected by the other authors here re- 
viewed. The chief objection urged against it, which is pre- 
sented, as before noted, by Kendall and Gray, consists in an 
approximate identity of level with that of to-day having 
been held by some drift-bearing areas at a time very shortly 
preceding their glaciation. This is clearly known to have 
been true of portions of Great Britain and of New England. 
In respect to this objection, it must be acknowledged that the 
preglacial high elevation which these areas experienced was 
geologically very short. With the steep gradients of the Hud- 
sun, of the streams which formed the now submerged chan- 
nels on the Galifornian coast, and of the Congo, these rivers. 
if allowed a long time for erosion, must have formed even 
longer and broader valleys than the yet very impressive 
troughs, continuing to depths of 2,000 to 6,000 feet beneath 
the sea level, which are now found on these submarine conti- 
nental slopes. But the duration of the epeirogenic uplift of 
these areas on the border of the glaciation for the Hudson, 
beyond it for the California!! rivers, and near the equator in 
western Africa, can scarcely be compared in its brevity with 
the prolonged high altitude held during late Tertiary and 
earl}- Quaternary time by the Scandinavian peninsula and by 
all the northern coasts of North America from Maine and Pu- 
get sound to the great Arctic archipelago and Greenland. 
