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BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



It is noteworthy that here, as in the neighborhood of Lee's Ferry, 

 landslides have taken place where the blue clays have been uncovered 

 by the encroachment of the eastern platform on the base of the Triassic 

 cliffs. This was the case just west of Pipe spring, where the former 

 head of the western platform has been deeply undercut. The blue clays 

 were seen here and there along the base of the refreshed cliffs, and 

 several landslides were noted in the same small district (L, Figure 6). 



Relation of the Pipe Spring Divide to the Pipe Spring Fault. — An- 

 other peculiar feature of the eastern platform near Pipe spring is that 

 it crosses the line of the Sevier-Toroweap fault (see that section) with 

 unbroken grade, and that its descent is against the heave of the fault ; 

 that is, from the relatively depressed block of the Uinkaret to the rela- 

 tively uplifted block of the Kanab plateau. No topographic indication 



Figure 7. 

 View north near Pipe spring. Vermilion cliffs of Triassic plateau in background: the 

 eastward dip of strata toward the Sevier-Toroweap fault-line is seen on the right, Pipe 

 spring being near the end of the cliffs. The "wall" of the migrating divide sweeps 

 through the middle of the landscape. Drawn from a sketch. 



of the fault is preserved at this locality, because the weak lower Trias- 

 sic shales on the west are brought against the weak Permian shales on 

 the east. The obliteration of the fault, as far as the relief of the sur- 

 face is concerned, is an unusual feature of the plateau region, according 

 to Datton ; for while he noted the obliteration of the Shinarump escarp- 

 ment in the neighborhood of Pipe spring (c, p. 80) he did not connect 

 its disappearance with any dislocation, and he elsewhere remarked that 

 " every fault in the district is accompanied with a corresponding break 

 in the topography" (c, p. 130). It should be stated that we identified 

 tbf geological formations mentioned here and elsewhere entirely by 

 their location, their lithological features, and their succession, as de- 

 scribed in Dutton's reports, which in this way, as in so many others, 

 were of the greatest service at every turn. Most of the formations are 



