174 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
mountain base; it receives strong support from the abundant evidence 
of the recently continued movement on the fracture by which the depres- 
sion and the mountain block were originally outlined. The evidence to 
this end is interesting from its variety and its accordance. 
Graded valley floors of moderate width dissect the mountain side, but 
their floors he one hundred or two hundred feet above the plain; the 
valley streams have now entrenched narrow ravines in the valley floors, 
and thus flow out upon alluvial fans at the mountain base. The spurs 
between the ravines are of rounded, full-bodied form; they do not taper 
away on the plain, but are rather sharply cut off by the basal slope of 
the mountain. The upper surface of the spurs is maturely graded, but 
their lower slopes are often gashed or ‘ripped ”’ by little gullies, sugges- 
tive of active erosion ; the color of the spur slopes is therefore prevail- 
ingly lighter than that of the spur tops. Many of the fans are broken 
by low scarps closely in line with the mountain base; this indicates a 
continuation of faulting into a very recent period. Some of the fans at 
the northern end of the western base of the range seem unusually low, as 
if the plain there had been depressed while the mountain was rising. 
Taken all together, one can hardly imagine more satisfactory evidence of 
block faulting. 
It should be noted, however, that the higher parts of the mountain 
seem to have been abundantly dissected since the faulting began. 
The west-facing scarp of the basalt sheet is now a mile or more back 
from the west-facing scarp of the underlying strata, but the accordant 
outlines of the two scarps strongly suggest the original definition of both 
by the same surface of fracture. Deliberate and detailed study of this 
range would well repay the observer who could undertake it. 
