248 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
of these are broken sharply in two as at Bellevue, at the mouth of the 
Virgin canyon, and at Sugar Loaf along the Hurricane, and at the | 
southern end of the buttes in the middle portion of the Grand wash. 
Others, such as those at Toquerville on the Hurricane and at the 
northern end of the’ buttes in the Grand wash, are highly flexed into 
attitudes which liquid sheets of lava could not possibly assume, and 
therefore must have been bent into their present position by movements 
of the crust. In addition to this evidence from lava flows the fault 
scarps themselves show signs of being very recent. They are almost 
always ungraded and precipitous, and run across country with utter 
disregard to structure or drainage. A third proof of recency lies in the 
fact that the strata on the two sides of the modern faults match per- 
fectly when restored to the level that they occupied before the faulting 
took place. In regions where faulting took place long ago the 
outcrops on the two sides have retreated at unequal rates and do not 
match. 
The relation of this recent faulting is well understood in the case of 
the Hurricane fault, where, as we have seen, the topographic results 
of the earlier faulting were almost entirely effaced during the long inter- 
fault cycle. The later faulting followed closely the general line of the 
other, but, contrary to what would be expected, often diverged from 
it slightly for long distances. Thus, though the two run closely parallel, 
they do not coincide, and sometimes cross one another as at Kanarra. 
In the Grand Wash fault the relation between old and new is not so 
clear, because, on account of the inaccessibility of the region, our knowl- 
edge of it is very slight. Our own observations applied almost entirely 
to the distinctly modern faulting. Gilbert, however (a, p. 54), gives an 
east and west section along the mouth of the Grand wash which shows 
that the total displacement is decidedly greater than that which our 
observations show to be due merely to the new fault. The logical 
inference is that there was an earlier Grand Wash fault corresponding to 
the earlier Hurricane fault. Davis (0, p. 147), on the basis of facts 
stated in Dutton’s atlas and monograph, states that “ while a monoclinal 
slice of the Trias is preserved along the thrown [western] side [of the 
Grand Wash fault], there is no Trias on the heaved Shivwits block for 
fifty miles. The Trias must have once extended eastward beyond the 
line on which the fault was broken, and the uplifted eastern extension 
of the formation must have been worn away after the faulting.” The 
erosion which could remove such an extent of strata from the uplifted 
block must have required far more time than has elapsed since the 
