160 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
deductions of specialized types could be confronted. It may be noted, 
however, that the deduced features of the back slope of a tilted block are 
not so much unlike the forms of residual mountains as are those of the 
front of such a block. It is, therefore, not-to be expected that tilted- 
block ranges can be recognized so well when their back is seen as when 
one looks at their expressive face. But when the features characteristic 
of the back slope of a tilted block occur on one side of a range while 
those appropriate to the faulted face occur on the other side, it is rea- 
sonable to look upon such a range as the result of block faulting. 
The eastern side of the Santa Rosa mountains north of Winnemucca, 
Nevada, for example, does not imitate the well-defined base line of the 
western side, so far as I saw this range. The eastern valleys are open 
and well graded between spaced spurs. The same is true of the eastern 
base of Jackson range, whose western base has already been mentioned 
as suggestive of faulting. Moreover, in profile this range resembles a 
tilted block when seen from the north in such a way that its ravines 
are hidden behind its spurs. The crest line is near the western side 
where the slopes are precipitous, while the eastern slopes are much more 
gradual. 
If any ranges have been carved from uplifted blocks, bounded by 
faults on both sides, they have —so far as the examples that I saw are 
concerned — reached the advanced stage of dissection in which the initial 
upland is carved into a serrate ridge. My line of travel seldom made it 
possible to see both sides of a single range, and hence my notes leave 
it uncertain in most cases whether a range with a well-defined base 
line on one side is similarly formed or not on the other side. 
Modern Faulting. — It is certainly very significant that indisputable 
evidence of modern displacement should be found close along certain 
mountain base lines where abundant evidence of long-continued earlier 
faulting is provided by the mountain form. This has been so clearly 
pointed out by Gilbert and Russell that little space need be given to it 
here. Suffice it to say that repeated instances of scarps in gravel deltas 
and fans were noted last summer along the Wahsatch base, as well as 
along the border of certain other ranges to be described below. A dis- 
tinct scarp in the gravels of the Bonneville beach is traceable all along 
the front of the Spanish Wahsatch, a little forward from the base of the 
facets, — Plate 1, a. The breaks in the delta of Rock canyon creek 
and in various other gravel deposits near Provo were easily recognized. 
It is sometimes suggested that the displacements in the Bonneville 
gravels are more of the nature of superficial landslides than of deep- 
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