74 
GILBERT. 
The Appalachian and Rocky mountains and the Wasatch 
plateau all appear to be of the nature of added loads, the 
whole mass above the neighboring plains being rigidly up¬ 
held. The Colorado Plateau province seems to have an ex¬ 
cess of matter, and the Desert Range province may also be 
overloaded. The fact that the six stations from Pike’s Peak 
to Salt Lake City, covering a distance of 375 miles, show an 
average excess of 1,345 rock-feet indicates greater sustaining 
power than is ordinarily ascribed to the lithosphere by the 
advocates of isostasy. 
It indicates also that the district used in this discussion 
for estimating the height of the mean plain, is far too small ; 
even the radius of 100 miles selected by Mr. Putnam may 
not be large enough. 
Future Work .—In my judgment it will be advantageous 
to give early place in future work to a group of stations so 
arranged as to yield data for the discussion of the proper 
method of computing the mean-plain or Faye correction. 
For this purpose a district of bold relief is preferable and a 
contour map is essential. The requirements are probably 
best met in the Rocky mountains of Colorado. 
It is a question of great interest whether the central part 
of the Great Basin, a broad district of ancient and modern 
corrugation, but without net gain or loss from surface action, 
is in equilibrium. Its discussion requires a chain of stations 
from Promontory, Utah, to Wadsworth, Nevada. 
The postulated isostasy of the interior plain is of such 
importance as to deserve further test. If really in equi¬ 
librium the plain not only gives a standard of reference for 
other districts, but affords a valuable field for the redetermi¬ 
nation of the latitude constant of the formula for local grav¬ 
ity. I suggest a set of stations in North Dakota and Mon¬ 
tana and another set in Texas. The Texas set might also 
be compared with a set in Louisiana for the purpose of con¬ 
trasting gravity in regions of rapid degradation and rapid 
deposition. 
