( 7 ) 
Nevada, the western half of Utah, and probably a large part of 
Idaho. These changes involved movements upon three lines of 
faulting. Of these one is the Wahsatch fault, on which we know 
that previous movements had taken place in the Archaean. The 
second also runs in a northerly and southerly direction crossing 
the fortieth parallel at about longitude 117 0 . Here too, motion 
must have occurred during the Archaean, since otherwise the Palae¬ 
ozoic sea could not have found a shore at this limit. The third 
line of fracture is close to the present position of the Sierra 
Nevada and probably passed along its eastern flank. Fig. 2 
shows the relative positions of the sea and land at the close of the 
Palaeozoic along the fortieth parallel. 
The next period after the Palaeozoic is known to geologists as 
the Jura-Trias. During this time strata were deposited to the 
east of the Wahsatch and between the Sierra Nevada and longi¬ 
tude 117 0 . These two seas, however, appear to have been with¬ 
out connection, and the animal remains which they contain are 
not identical. The fossils in the more western area however are 
few in number, imperfect and unsatisfactory. 
At the close of the Jura-Trias the bottom of this western sea 
rose again, new movements taking place along the Sierra Nevada 
and the line of disturbance at 117 0 . This western Jura-Trias 
sea was thus obliterated. At the same time the Pacific coast 
sank beneath the waters of the Pacific Ocean. The fault along the 
Sierra Nevada on this occasion does not appear to have taken 
place at its eastern base but along its western flank nearly in the 
position of the gold belt of California. Its northern extension ran 
along the Blue Range to the north-eastward. The section along 
the fortieth parallel after these changes, is represented by Fig. 3, 
from which it appears that to the east of the Wahsatch the condi¬ 
tions were unchanged. 
After the Jura-Trias comes a period called the Cretaceous, 
because most of the chalk of Europe was deposited during this 
era. Very early in this period a new change occurred. The 
coast ranges of California and the cascade range of Oregon were 
driven up, while a large addition was made to the western flank 
of the Sierra Nevada. This upheaval was extremely violent. 
Most upheavals are so slow that the strata of rock, once horizontal, 
