DAVIS: MOUNTAIN RANGES OF THE GREAT BASIN. 143 
contrast with the Ombe and Ute ranges, south and west of Tecoma: 
both of these are of strong relief, with relatively rectilinear base lines 
on the sides toward the railroad. Their valleys are steep-sided and 
narrow-floored, causing but little interruption in the otherwise continu- 
ous mountain front. Nevertheless, these higher ranges have been 
abundantly carved, so that their peaks and spurs preserve no indication 
of an original block form; and no signs of modern faulting, elsewhere 
so easily recognizable from the train, were here visible. 
North of Omar, there is a typical subdued mountain mass, whose 
dwindling spurs interlock with open valleys. This example was strongly 
contrasted with the lofty Humboldt range, south of Wells; here the 
snow-patched peaks descended by strong slopes to a relatively rectilinear 
base line on the northwest. 
Northeast of Golconda, Nevada, a low range descends to a very ragged 
base, one of the best examples of the kind that my trip discovered. Its 
description would involve a repetition of what has just been said for other 
similar ranges, though the description here might be somewhat more em- 
phatic than before. 
The only example of this class which I photographed was a small un- 
named range, about forty miles north of St. George, Utah, here repro- 
duced in Plate 7,38. Its spurs were long drawn out, with concave 
profiles toward their base ; its valley mouths were wide open, holding broad 
waste-covered slopes. Its base line was sinuous and indefinite, in the 
strongest contrast to the simple and definite base line of the Spanish 
Wahsatch, Plate 1, bs. 
The Canyons and Ravines of Block. Mountains. — If we now return to 
the consideration of the higher Basin ranges, it seems undeniable that 
faulting gives a much better explanation of their base line than can pos- 
sibly be given by erosion. Indeed, erosion can be appealed to for the 
removal of the missing mountain masses only so long as the processes and 
results of erosion are looked upon as arbitrary and beyond reduction to 
those generalizations known as natural laws. The day has passed when 
this is permissible. Erosion, whether subaerial or littoral, fluvial, glacial, 
or eolian, proceeds systematically through a series of stages; and while 
there is still more to be learned than is now known regarding the progress 
of mountain sculpture, enough is already safely understood to exclude the 
resort to erosion in general as a ready means of accounting for any de- 
sired result. It remains, however, to be seen whether not only the base 
but the face of the Basin ranges is consistent with the theory of block- 
faulting. The form of the valleys that are carved in the mountain face 
VOL. XLII. —NO.3 2 
