bo 
CHARLES. R. .KEVES 
(SS) 
Spurr’ appears to be the first to bring into serious question the 
early explanation of Gilbert’s, afterward adopted by King, Powell, 
Russell, and others,? regarding the simple fault-block origin of the 
Basin ranges. ‘This author considers stream-corrasion as the most 
important or only sculpturing agency, but he expresses the opinion 
that erosion and upheaval have gone on together, more or less uninter- 
ruptedly ever since Jurassic times, the mountains being eroded from 
a folded substructure in the same way as in the case of the Appala- 
chians, when the precipitation was much greater than at present, while 
“subsequently the climate became arid and the water-supply was 
not sufficient to remove the detritus from the valleys, which filled 
up.” This view, however, as will be seen later, does not appear, 
according to Davis,3 to be sufficiently supported. 
The idea of the Basin ranges presented by Davis‘ recently is that 
they are “dissected fault-block mountains.’’ The descriptions, and 
illustrations which accompany them, indicate clearly that the moun- 
tains are regarded as blocks first upheaved and tilted and then sub- 
jected to rapid corrasion by the mountain torrents, the intermont areas: 
being deeply filled by the rock-waste of the contiguous highlands. 
This is practically Gilbert’s hypothesis theoretically considered in 
its essential consequences, accompanied by the definition of some of 
the criteria by which the stages of dissection of a fault-block mountain 
may be recognized. 
The Great Basin taken alone presents many difficulties to a clear 
interpretation of some of its most characteristic features. Farther 
south in the desert region, at the northern end of the Mexican table- 
land, there are displayed certain phenomena which seem to offer 
critical evidences bearing upon the question in hand. A few years 
ago I incidentally referred’ to the probable significance of some of 
these features and to the physiographic evolution of that part of the 
country, regarding the region as a peneplain that had been uplifted 
in mid-Tertiary times, broken into high blocks, and then subjected to 
t Bull. Geol. Soc. America, XII, p. 217, 1gol. 
2 Geog. and Geol. Expl. and Surv. W. 100 Merid., Prog. Rept., p. 48, 1874. 
3 Science, N. S., XIV, p. 457, Igor. 
4 Bull. Mus. Comp. Zodl., XLII, p. 131, 1903. 
5s American Geologist, XX XIII, p. 22, 1904. 
