62 
OROGENY AND EARTH’S ROTATION 
ever drifting desert sands and to be only thinly covered by soil. 
Instead of desert ranges rising higher and higher as their loads 
are lightened it was demonstrated that their summit depletion is 
inappreciable; and that they grew taller because the surrounding 
general plains-surface underwent rapid lowering. Under the 
stimulus of aridity regional lowering and down-cutting appeared 
to go on without regard to the sea, and, provided the waters of 
the latter are kept out, excavation seemed capable of proceeding 
indefinitely. 
When the theory of isostasy was first advanced the conception 
of a geographic cycle for all land-forms had not yet been develop¬ 
ed, a distinct desert geology was not yet known, and the tran¬ 
scendent effects of the wind, when under the stimulus of aridity, 
was undreamed. Many, if not the majority, of desert relief 
phenomena which were thought to find satisfactory explanation 
in isostasy were later found to fall completely under other influ¬ 
ences. In the end isostasy presented the paradox of the more the 
mountain tops were worn off the higher they floated. 
In all descriptions of the Great Basin ranges it seems utterly 
impossible to divorce the consideration of the mountain sculpture 
from that of the orographic structure. The two are always treat¬ 
ed as if they were identical, or as if they were at least dependent 
upon each other. That the one is not in any way the genetic out¬ 
growth of the other is conclusively shown by recent critical obser¬ 
vations having this point particularly in view. Dr. J. E. Spurr 
astutely observes cencerning the Nevada ranges that no one has 
ever seen the fault-lines which are assumed so universally to 
bound the desert mountain-blocks. In this statement he touches 
on the crux of the whole problem of the origin of the Basin ranges. 
When the impression was first gained that the desert ranges 
were simply tilted fault-blocks critically supporting evidence was 
strangely wanting. Finally, when the testimony was especially 
sought it was found that profile and structure held no direct rela¬ 
tionships to each other. Among the Great Basin mountains this 
independence of profile and structure proved to be particularly 
notable.^^ These relationships were unusually well displayed in 
such ranges as the Humboldt, White Pine, Funeral, Vegas, Spring 
Mountain, Grant, and Hot Creek mountains. 
22 Bull. Geol. Soc. America, Vol. XXI, p. 55(>, 1910. 
