J. LeConte—WStructure and Origin of Mountains. 101 
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esse) SAS Se 
closely appressed folds such Ideal diagram showing probable st 
1 ave formed the of the Sierra Nevada range. 
Sierra Nevada, showing the grand wave composed of enormous 
thickness of sediments, the subordinate wavelets, composed of 
the upper crumpled portions of the series, the lower portions 
being metamorphosed into granites and exposed along the axis 
by erosion. 
Again: the Sierra range is an admirable example of a fold 
passing gradually into a fault. In the northern portion of Lake 
Tahoe the slates occupy a broad area on both slopes, though 
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ie> 
ructure 
more unequal and the crest higher, viz: 138,000 feet. The 
great wave is ready to break (fig. 12,6). In the southern portion 
about Lake Owen, the eastern slope is still more abrupt, the 
eastern slates have entirely disappeared, granite alone forming 
the summit and the whole eastern wall, and the crest here 
reaches its highest point, near 15,000 feet. The great wave has 
at last broken with the formation of a prodigious fault (fig. 12, ce). 
membering that the escarpment is here 10,000 to 11,000 feet, 
and that the whole thickness of the slates has been removed by 
erosion from its summit, and that their eastern continuation lies 
buried beneath the soil of the plains below, we cannot estimate 
this slip as less than 15,000 feet. It is probably much more. 
It is almost certain that it 
was a slight re- adjustment 
of this slip which caused the 
hyo earthquake of March, 
1872. In fig. 12, a, b, ¢, are 
generalized sections repre- 
senting these facts. It is on 2 
the steep slope side, or else along the crest, that all the great 
Voleanic outbursts have occurred. This is exactly what we 
Am. Jour. ioe Raises ar. Vou. XVI, No, 92.—Aveusr, 1878. 
