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, b, p.. 198; Gilbert, d, 

 p. 341). The most recent studies of the ranges by Spun*, 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 

 che 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 



