144 



BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



erosion since faulting are generally indicated by a break in the align- 

 ment of the Triassic and Shinarump cliffs wherever the fault lines cross 

 them. Powell (a, p. 191), Gilbert (a, p. 51) and Button (c, p. 200) 

 all recognize the greater recession of the escarpments of the heaved side 

 of the faults as a general occurrence, but they do not explicitly connect 

 the amount of recession with the date of faulting. The dislocation of 

 the cliff front is, as Gilbert phrases it, " not due to any horizontal 



. -.Pipe Spr. / 



_UTAH 

 ARIZONA »k& 



^^at•"" , " ,, •"'*' 



9 ''n*....Jy.k 



*'wi i <*• 





t^xi'ito- I'"'""*' FYe.donia 



'^mi/% 



Antelope fi 

 Valley 



: O 



s 



10M 



Figure 11. 



Sketch map of the Pipe spring district, showing the Sevier-Toroweap fault. Weak lower 

 Triassic strata, dotted; Triassic and Shinarump cliffs, hachured. Constructed from 

 Dutton's map and original field notes. 



displacement along the line of fault, but merely to the fact that the 

 eastern portions, being lifted higher than the western, became subject 

 to different conditions of denudation" (a, p. 51). Near Pipe spring, 

 not only have the cliffs of the eastern (Kanab) block receded ten miles 

 since the faulting occurred : but ten miles is the excess of the recession 

 of the eastern cliffs over that of the western ; hence the chief movement 

 of the fault here must certainly be of earlier date than the beginning of 



