146 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



retreat of the revived cliff" from the fault line has sometimes given rise 

 to the belief that the fault is of recent date, but it is evident that no 

 such conclusion can hold. The revived cliff may be in the thrown- 

 block, if the arrangement of the rocks favors such a result. A striking 

 example of this kind may be seen in Tennessee (see Briceville, Tennes- 

 see, topographic sheet, United States Geological Survey), where the front 

 of the Cumberland plateau is cut across by a northwest-southeast fault, 

 the northeastern block being relatively uplifted ; but to-day the surface 

 is worn low on the weaker strata of the uplifted block, so that it is over- 

 looked by the uplands of Carboniferous sandstones on the depressed 

 block. 



If these considerations are accepted, there can be little doubt that the 

 Sevier fault continues in strong force beyond Pipe spring, as if to join 

 the Toroweap fault, some thirty miles further to the southwest. Some 

 topographical expression of the fault ought to be found in the broad 

 floor of Antelope valley, beyond the Shinarump cliffs of the Uinkaret 

 plateau, where the weak Permian of the Uinkaret block lies opposite 

 the resistant upper Aubrey of the Kanab block. It is perhaps in this 

 way that one may explain a west-facing bluff which extends about ten 

 miles south of Antelope valley (Dutton, c. Atlas, sheet XXII.), but 

 further study on the ground is needed before this can be assured. It 

 is interesting to note, however, that the wet-weather drainage here is 

 from the weaker beds of the thrown block eastward through a gorge in 

 the bluff that is determined by the more resistant beds of the heaved 

 block ; a condition that is again entirely inconsistent with a recent 

 movement on the fault plane. 



The Hurricane Fault is not definitely dated in Dutton's report, but its 

 southern part is thought to be of " comparatively recent origin," be- 

 cause " the amount of recession by erosion of the cliff of displacement is- 

 very small" (c, pp. 116, 117). Its northern part near Virgin river 

 must, however, be old enough to have allowed a strong recession of the 

 Triassic escarpment since the faulting ; for the two parts of the Trias 

 east and west of the fault line are now fifteen miles apart (c, pp. 42, 

 200); and as in the Sevier-Toroweap fault, the displacement of the 

 cliff's is a measure not merely of their erosion since faulting, but of 

 the excess of erosion in the heaved block over that in the thrown. The 

 small amount of recession of the Hurricane ledge (Aubrey) from the 

 fault line in the southern part of the Uinkaret plateau, as stated in 

 the last quotation from Dutton, may be explained not so much by the 

 recent date of the fault, as by the recent date at which erosion had 



