MOHAWK LAKE BEDS. 
399 
In 1878, in his article on the “ Structure and Origin of 
Mountains,” (XIX, pages 100-101), Professor Le Conte 
says : 
“ 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. * * * So simple appears 
the structure of this mountain that we might imagine that 
it consists of only one grand fold, eroded along its crest until 
the granite is exposed. * * * But this is probably not 
so, because forty miles of slates and schists outcropping at 
high angle would give an incredible thickness of sediments 
if we regard them as a single unrepeated series. It is prob¬ 
able, therefore, that these flanking slates really consist of 
several closely appressed folds, afterward deeply eroded so 
as to simulate a single series. * * * 
“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 largely covered on the eastern slope by volcanic ejec¬ 
tions. The two slopes are more equal, and the height of the 
crest is moderate—only about 9,000 to 10,000 feet. The 
great wave [referring to the largest supposed fold forming 
the crest of the range] is more normal. 
“ In the middle portion, about Lake Mono, the eastern 
slate area is far narrower, the two slopes more unequal, and 
the crest higher, viz., 13,000 feet. The great wave is ready 
to break. In the southern portion, about Lake Owen, the 
eastern slope is still more abrupt, the eastern slates have en¬ 
tirely 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. Remembering 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 soils of the plains below, we cannot esti¬ 
mate this slip as less than 15,000 feet. It is probably much 
