PHYSICAL GEOGRAPHY OF THE PLEISTOCENE 591 
precision, the best opinion seems to place it, or at least its initiation, 
in the late Pliocene and early Pleistocene. 
Students of the western interior have reached no general agree- 
ment as to the amount of late Tertiary and Quaternary change of 
level, but there is general agreement that the land of that region was 
notably higher at the close of the Tertiary, and later, than it had been 
before. ‘The increase in the height of the land amounted, perhaps, to 
a few thousand feet in some places, but was probably far from uniform. 
4. In the West Indies and Central America, the interpretation 
of facts and supposed facts seems to be more or less uncertain. 
Spencer would make the amount of change of level in the West 
Indies within this general period very great, even 8,000 to 11,000 
feet higher than now. Hill would have some portions of Cuba at 
least 2,000 feet higher than now at or since the close of the Tertiary, 
and the Barbadoes 1,100 feet higher at about the same time, while 
Hershey thinks the Isthmus of Panama has been bowed up 1,000 
feet or so since the beginning of the Pleistocene. 
If even the more moderate of these figures are correct, it appears 
that the average relative increase in the altitude of the continent 
must have amounted to several hundred feet at least. This amount of 
elevation must have been adequate (1) to increase erosion by streams 
greatly, this increase resulting both from (qa) increase in precipitation, 
and (0) increase in gradient of the streams; (2) to lower in some slight 
measure at least the average temperature of the land, and to increase 
its range; and (3) to reduce the amount of vegetation on the average, 
both because of (a) the unfavorable change in temperature and (b) the 
more rapid erosion. 
Outside of North America, similar changes seem to have been 
in progress. ‘Thus in South America, such determinations as are 
at hand point to an elevation approaching 3,000 feet at a maximum 
on the west coast of South America, since the late Tertiary. Changes 
of similar import, and perhaps of comparable extent, are indicated 
by the facts reported from other continents, though for all but Europe, 
the facts are meager. In Europe, changes of level at the close of the 
Tertiary were not everywhere great, but about the borders of the Alps, 
the increase of elevation is estimated by Penck and Briickner to have 
been 300 to 500 meters. 
