100 J. LeConte—Structure and Origin of Mountains. 
their former existence and place. These are in fact extinct 
cosa: eae forms are gone; only their buried and fossil- 
ized skeletons remain. 
Again: in all mountain ranges, but especially in those of 
this type, the great swell constituting the range, and often also 
the subordinate wave ets, are unsymmetrical, the slope on one 
side being long and gen ntle, and on the other short and abrupt. 
The crest is near one side: the wave is, as it were, ready to 
break, or has already broken. This asymmetric form has 
mountains is admirably shown in the Sierra, the a- 
lachian, and to a less extent in the ay be 
reg as the typical form of a monogenetic upheaval 
oun 
The Sierra Nevada may be taken as a typical example both 
in form and in structure of a monogenetic upheaval, or what I 
have called a Range. As to form: this range rises on its 
western side from the San Joaquin plains, only about a hun- 
dred feet above sea level, by a very gradual slope of fifty to 
seventy miles in length, until it ieee a crest 12,000 to 15,000 
feet in height, and then plunges down by a steep slope which 
reaches the plains of Lake Mono, or Owen’s River valley 5,000 
feet high in sixor seven miles. As to structure: it consists of a 
granite axis twenty to twenty-five miles wide, flanked on 
either side by slates and schists dipping at a high angle. Fig. 
10 is a generalized section of the Sierra, from the San Joaquin 
plains, 8. J. P., to Lake Mono, L. a , Showing the typical con- 
our of a mountain range. 
On the long western slope 
the slates and schists outcrop 
= so = =] many parts, in fact, = er- 
yay on across Sierra Mount rt 
from San kaso. plains to Lake Mono. a Ging the ct en _ pa 
occurs a broad interval of granite, twenty to twenty-five miles 
wide, after which the slates reappear, forming the highest sum- 
mits, such as Mounts Lyell and Dana, and the whole eastern 
slope So simple appears the structure of this mountain, that 
might imagine that it consists of only one grand fold, eroded 
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