104 J. LeConte—Structure and Origin of Mountains. 
about Salt Lake 4,000 feet high in two miles. The east walls 
of the faults formed here are 12,000 feet in the air—the west 
walls lie buried beneath the soil of the plains . 
e same horizontal thrust which sushed up the Wahsatch 
also arched the stiffened land crust of the basin region and 
formed the north and south fissures and faults of that region. 
The basin ridges therefore probably belong to the same time. 
d. In passing from the lowest foot-hills, bordering on the 
San Joaquin plains, to the granite axis o 't e Sierra, we pass 
from fine fissile clay-slates through schists of increasing coarse- 
ness to granite. This is doubtless partly the result of increas- 
etamorphic change in this direction. But it is also, I 
believe, largely due to a change in the character of the original : 
sediments. If the eastern base of the Sierra was once a shore- 
line, then coarse sandy sediments would have been deposited 
there while only fine clays and silts would be carried farther 
out to sea. The metamorphism of the more siliceous material 
nowhere, as “far as I know, consist of pure and fine argillaceous 
matter like those of the western foot-hills. In the formation of 
this mountain it seems probable that the finer and softer clays 
at some distance from shore in yielding would be thrown into 
many small folds, while the somewhat firmer sands nearer 
shore, though yielding the most beneath, because thickest and 
therefore most softene aqueo-igneously, would rise as one 
simple fold, whieh would then be pushed over and perhaps 
break on the Jandward side. I believe it is very important 
from this point of view to compare carefully the strata on the 
two sides of mountain ranges. If mountain ranges are up- 
swelled marginal sea-bottoms, then the strata on the two slopes, 
though corresponding in age, and in fact originally continuous, 
ought not to correspond in lithological character. I believe we 
have here an answer to Studer’s objection to Lory’s theory of 
fan-structure (fig. 8), viz: the non-correspondence of the strata 
on the two sides of the crest. 
Il. Origin of Mountains. 
In all I have thus far said I have assumed that mountain 
ranges are formed by horizontal pressure in the manner and 
iene - 
appear. By no effort of the imagination can we even conceive 
* Emmons, Survey of 40th parallel, vol. ii, p. 340 and seq. 
