400 
TURNER. 
more. It is almost certain that it was a slight readjustment 
of this slip which caused the Inyo earthquake of March, 1872. 
“ Marginal sea-bottom sediments are thickest near shore, 
and thin out very gradually seaward. Such sediments, there¬ 
fore, even before yielding, form a lenticular mass, with the 
thickest part near the shore edge, and therefore asymmetric. 
Now, this already thickest part is precisely the line of great¬ 
est yielding and therefore of greatest ups welling, and thus the 
mountain wave becomes very asymmetric, with its steeper 
slope landward. Finally, the already asymmetric mountain 
is pushed over against the stiffened land crust, making a 
still steeper slope, which may even break on that side. 
“ Now, the Sierra is again an admirable illustration of this 
law. The oldest portion of the western half of the American 
continent is probably the basin region, especially its south¬ 
ern portion, running down into Mexico. During much of 
the Paleozoic and all the Mesozoic times until the end of the 
Jurassic this was a continental mass with its western shore 
near the eastern margin of the Sierra region. The Sierra 
region, as I have elsewhere shown, was then a marginal sea 
bottom, receiving sediments from the basin-region continent, 
until an enormous thickness had accumulated. When these 
thick sediments began to yield from the aqueo-igneous soften¬ 
ing of their floor they would first swell up asymmetrically, 
and then be pushed over against the stiffened Basin region 
land crust, forming a steep slope, or even a fault and escarp¬ 
ment, on that side.” 
Professor Le Conte, in the same paper, ascribes a similar 
origin to the Wahsatch Mountains, which he regards as 
made up of sediments, on the eastern shore of the basin- 
region land mass, while their steep western and landward 
escarpment was formed in the same way that the steep 
eastern and landward escarpment of the Sierra Nevada was 
formed. 
In 1880 Professor Le Conte wrote an important article on 
