DAVIS: THE WASATCH, CANYON, AND HOUSE RANGES. 27 
and denuded structures, which are now warped upward in one direc- 
tion to a mountain crest, are warped downward in the other direction 
and descend beneath the floor of an aggraded basin. ‘The base line 
of such ranges does not accord with structural lines; the quaternary 
deposits, that have been supplied to the depressions or basins by the 
erosion of the uplifted areas, lap unconformably on the mountain 
Slopes and irregularly cross whatever structures have there been 
bent down. This kind of discordance between structural features 
and mountain base is repeated on a larger scale along the western 
border of the Sierra Nevada, where the Quaternary deposits of the 
Valley of California lap over the down-warped surface of the denuded 
Mountain mass; and again on the southern side of the Alps, where the 
Quaternary deposits of the Plain of Lombardy overlap various de- 
nuded belts of the mountain-making rocks. A border line of this 
kind might be expected on the back slope of a tilted Basin-range 
block. The simplicity of the border would depend in large measure 
on the faintness of relief of the block surface before faulting took place. 
The front border of a fault block range would resemble the first of 
the two previous types in respect to its relatively simple base line, 
but would differ from it in presenting no essential relation between 
base line and structure; 1t would resemble the second type in possess- 
Ing a base line that ran indifferent to the structure of the mountain 
mass, but would differ from it in the greater abruptness with which 
the mountain front would rise over the piedmont plain. 
It thus appears that various types of mountain border and base 
line are appropriate each to its own origin and history. Hence on 
returning to the Wasatch mountains with these various examples 
In mind, one is all the more convinced that continued upfaulting and 
elaborate carving of a mountain block give the only adequate explana- 
tion for such a cleft anticline as is found in the Provo mass, with its 
simple base line and sharp cut canyons; for such a carved escarp- 
ment of nearly horizontal strata as is seen in the Spanish peak mass, 
with its gracefully curved base line, its facetted spurs, and its narrow- 
mouthed ravines; or for such an obliquely truncated monocline as 
IS presented in the Mt. Nebo mass, with its obliquely carved ridges 
and valleys, its facetted spurs, its spilled weak strata, and its con- 
tinuous recent fault along the mountain foot. 
It should be remembered however that the Wasatch is not prop- 
erly a member of the Basin range system. Whatever history the 
asatch range may have, we must not infer that the Basin ranges 
Necessarily have the same history. But on the other hand the evi- 
