342 TJie- American Geoloffist. May, 1897 
cause, of the cold and the ice accumulation" during the Gla- 
cial period. 
The foundation principle, that the crustal uplifts are due 
to the earth's slow cooling and contraction, being indeed its 
resultant deformation to tit the hard exterior to the plastic 
contracting interior, was earlier enunciated by Crosby,* from 
whom 1 receive this key revealing the much debated causes of 
the Quaternary ice-sheets. 
Permanence of Continents and Oceanic Basins. 
It is evident, from the foregoing statement of my theory of 
the source of the earth's energy exhibited in its great epeiro- 
genic oscillations, that these are wholly harmonious with very 
long geologic duration of the continents and ocean basins, 
which Dana first clearly saw and taught. 
At the same time, however, it seems probable and nearly 
sure that the crustal uplifts and subsidences, many times re- 
peated during the long geologic ages, in combination with 
various tracts of especial weakness in the crust, may have led 
to considerable changes in the boundaries and extent of con- 
tinental areas, so that some parts of these and of the deep sea 
may have interchanged their places. 
The Ciiamplain Depression terminating the Ice Age. 
The general parallelism of the events constituting the Ice 
age in North America and in Europe implies the synchronism 
and common cause of the glac.iation of both these large con- 
tinental areas. Further, it implies also a common and s}^- 
chronous cause of the departure of the ice-sheets, which on 
each continent was rapid, as shown by the character of the 
drift deposits, and was attended with the advance of a warm 
temperate flora and fauna near or even upon the borders of 
the wasting icefields. The Ozarkian uplift, we may therefore 
confidently conclude, was at least as extensive as these vast 
glaciated regions; and it may also quite probably have includ- 
ed the intervening ocean bed. Transitions of the earth's de- 
formation, aided by the immense weight of the ice-sheets, may 
have produced alternate waxing and waning of glaciation in 
some districts, and it should probably also be accepted as the 
explanation of more extended glaciation during some parts of 
*Proc. Boston Society of Natural History, 1883, vol. xxii, pp. 455-460. 
