590 ROLLIN D. SALISBURY 
t. In the eastern part of the continent, the land is generally 
thought to have stood higher than before by some few hundred feet. 
If the more extreme views of a few of the geologists who have studied 
this question are accepted, the excess of elevation over the present was 
a few thousand feet. 
2. In the larger part of the Mississippi basin, the gain in altitude 
was considerable, though still on a relatively moderate scale. In the 
eastern and central parts of the basin it is probably to be measured 
by a few hundreds of feet, rather than by figures of a larger denomina- ~ 
tion. There is some reason for thinking that the important topo- 
graphic features of the central Mississippi basin are chiefly of late 
Tertiary and post-Tertiary origin, developed from a late Tertiary 
peneplain now represented by the summits of the higher hills and 
uplands of the region, a few hundred feet above the general level in 
which the present valleys are sunk. It is true that these summits 
have sometimes been interpreted as remnants of a Cretaceous pene- 
plain; but this conclusion is not firmly established, and the alternative 
suggested above is entitled to consideration. 
3. In the west, the relative uplift in the closing stages of the 
Tertiary and early Pleistocene was greater. The estimates of the 
late Tertiary and post-Tertiary uplift here at one point and another 
range from several hundred feet to several thousand. ‘The figures 
are most definite and perhaps most satisfactory near the Pacific 
coast. In southern California, the uplift at this time has been 
estimated at 1,500 feet; in northern California, 1,500 to 2,000 feet; 
and in the Sierras at 3,000 to 6,000 feet. In Oregon, Pleistocene 
marine fossils are found up to elevations of 1,500 feet, while in and 
about the Cascade Mountains of Washington, an elevation of several 
thousand feet, maximum, seems to be well established. 
In British Columbia, the relative upwarp of the corresponding 
time has been thought to reach an amount comparable to that of the 
Cascade Range, while, farther north, most of the estimates point to 
less extensive changes. The old peneplain which is now at an eleva- 
tion of 6,000 to 9,o0co feet in Washington and British Columbia, is 
thought to descend to 4,000 or 5,000 feet far to the north. While 
the age of the deformation which brought the former peneplain of 
these northern lands to its present position has not been fixed with 
