162 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
all the faulting of the Basin ranges occurred at the time when their 
province was dropped to a less altitude than that of the plateaus by the 
production of great faults along the boundary of the two provinces ; the 
faulting of the ranges was probably a complicated process, but on the 
whole it is believed to be associated with the lowering of the Basin range 
province, rather than with the earlier stage of its general elevation. It 
may be noted that in the southwest (southeastern California) some of 
the Basin range blocks have been greatly worn away (Fairbanks, p. 70), 
while in the northwest (southern Oregon) some of the blocks are as yet 
very little eroded (Russell, a, p. 444). In general, however, the post- 
faulting erosion of the ranges has produced a mature dissection without 
altogether destroying the block outlines (Powell, 8, p. 198; Gilbert, d, 
p- 341). The most recent studies of the ranges by Spurr, reported at 
a recent meeting of the Geological Society of America, indicate that the 
faulting has been more complicated and longer continued than had form- 
erly been supposed. In certain cases, streams flow through instead 
of around the ranges of to-day, from which it may be inferred that at 
least some of the existing drainage of the province had been established 
before the range blocks were tilted up. 
The drainage consequent on the new topography produced by fault- 
ing is assumed to have taken the best course that it could find to the 
southwest. The chief discharge may have here and there followed pre- 
existent valleys, but with a reversed direction of flow (see extract from 
Powell, below). Many short-lived lakes may have been formed by the 
somewhat adverse eastward tilting that has been supposed to have 
accompanied the faulting of the blocks; but there does not appear to 
be any positive proof that the tilting may not have been produced at 
the earlier time of flexing instead of at the later time of faulting ; 
certainly the strata of the Marble platform dip gently eastward 
between the east Kaibab and the Echo flexures, and here the dip and 
the flexures seem to be of the same date. In any case, the drainage 
of a large area of northeastern country, floored with Cretaceous and 
Tertiary strata, seems to have been gathered at a favorable point of 
discharge ; namely, near the point where the Kaibab uplift had been 
greatest, and where the exposure of the weak Permian beds had caused 
the greatest break in the strong Triassic escarpment by which the 
interior country was enclosed. Westward from the Kaibab, the escap- 
ing drainage presumably followed the lowest line that it could find 
between the Triassic escarpment on the north and the general ascent of 
the stripped Carboniferous country to the south. Perhaps in some such 
