MOHAWK LAKE BEDS. 
403 
Professor Le Conte, on the evidence of Gilbert, Howell, 
and Pussell, considers the fault scarps of the great basin to 
be due to normal faulting, which he considers due to gravi- 
tative settling. He says: 
“ It is certain that the great normal faults which charac¬ 
terize the basin region, among which must be counted the 
eastern Sierra fault and the western Wahsatch fault, were 
produced in this way long after the orogenic crumpling had 
ceased.” 
Professor Le' Conte has still further elaborated methods of 
faulting in a paper “ On the Origin of Normal Faults,” pub¬ 
lished in 1889 (XIV). This may be taken as representing 
his present views. 
Professor Le Conte assumes the earth to have a solid 
nucleus surrounded by a liquid layer on which the crust 
floats. Lie says: 
“At the end of the Tertiary the whole region from the 
Wahsatch to the Sierra, inclusive, was lifted by intumescent 
lava into a great arch, the abutments of which were the Sierra 
on the one side and the Wahsatch on the other. * * * 
“ The arch broke down and the broken parts readjusted 
themselves by gravity into the ridges and valleys of the 
basin region, leaving the raw faces of the abutments over¬ 
looking the basin and toward one another. It must not be 
supposed, however, that this took place at once, but gradually , 
the lifting, the breaking down, and the re-adjustment going 
on pari passu” 
. “ The Sierra Nevada is a great crust-block heaved and 
slipped on the eastern side, forming there a great fault of 
15,000 to 20,000 feet vertical displacement, and this took 
place at the end of the Tertiary, accompanied by floods of 
lava.” 
/ 
It will be observed that Le Conte’s views have undergone 
a marked change since his first articles were published. 
Supposing his assumption of a liquid substratum to be cor- 
