234 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
topographic effect and hence to estimate their relative age. To the east 
at the top of the escarpment is the maturely dissected upland, to the 
west at the base of the slope is a broad intermont basin floored with 
waste brought down from the uplifted region around it.! The escarp- 
ment itself shows at the top the mature slopes of the undisturbed 
ancient surface ; farther down these gruw more rugged and ledgy under 
the influence of renewed erosion, and at the base is the straight step 
scarp of the modern fault. South of Kanarra these simple features are 
varied only by the texture of the rocks and the size of the streams. It 
is near this little Mormon village, however, that the old fault reappears 
after being concealed for many miles under alluvium and basalt. It 
will be remembered that the new fault here crosses the old cne at an 
acute angle shearing off the western and southern portion. To the 
north both faults can be easily traced. The long slender wedge between 
them is composed of strata which were overturned at the time of the 
early folding and now lie in inverted order with a strong westward dip 
(see Fig. 8). Dutton speaks of the overturned fold and complicated fault 
at Kanarra as showing an exceptional movement (a, p. 29). Along the 
line of the old fault between these reversed strata on the west and the 
very slightly inclined normal strata on the east the slope of the escarp- 
ment everywhere diminishes, forming a slight terrace or even a little 
depression contouring along the slope. This is due to the fact that on 
both sides of the fault lie soft strata, while above them is the great mass 
of the plateau on the one hand and the cuesta-like ridges of the hard 
Aubrey limestone and Shinarump conglomerate on the other. Thus it 
happens that the old fault which geologically amounts to many thousand 
feet, has been entirely effaced geographically and is even replaced by a 
valley. More than this, the valley was not only worn out along the 
ancient fault line before the period of the second faulting, but was also 
filled in part with gravel, and on the gravel was poured out a lava flood. 
That the lava was poured out before the last faulting is indicated by the 
fact that it lies horizontally on what is now a hillside, but was then a 
valley floor. Moreover the erosion consequent on the uplift at the time 
of the later faulting seems to be the only competent cause for the dis- 
section of the lava-covered gravel into flat-topped buttes, where the loosely 
cemented pebbles are protected from erosion by a sheet of basalt. The 
1 This plain lies at an elevation of about six thousand feet, and forms part of the 
divide between the interior basin and the Colorado river. It is so flat that several 
streams flowing out of the mountains are sometimes deflected northward to Sevier 
lake and sometimes southward to the Pacific ocean. 
