( 6 ) 
the Archaean, each portion of this region was under water and 
accumulated sediments. We have now no means of telling how 
land and water were distributed at any one portion of the 
Archaean. One important fact is known, viz. that during this 
period a great fault existed along the western flank of the 
present Wahsatch range. I shall show that there were probably 
other similar faults along other of the present ranges. 
During the Palaeozoic, Oregon, California, the western half of 
Idaho and of Nevada and the south western half of Arizona 
appear to have been for the most part dry land. How much 
further west than the present Pacific coast this continent extended 
we have no means of knowing. To the east of this continent 
lay a great sea in which there gradually accumulated an immense 
thickness of sediment later turned to rock, chiefly limestone. 
The Palaeozoic was a period of immense length and in the region 
under discussion a very quiet period, so that there is scarcety any 
evidence of disturbance in the deposition of sediment. There is 
nevertheless evidence of a very important and interesting move¬ 
ment. It appears impossible to avoid the conclusion that as the 
weight on the sea bottom increased, particularly near the coast in 
central Nevada, the bottom slowly sank under the weight as if 
the earth beneath it had possessed a plasticity similar to that of 
shoemaker’s wax. This, though in a vastly smaller degree, is 
almost certainly true. 
For the sake of making a rude comparison between the distri¬ 
bution of land and sea at different epochs, I have represented the 
conditions during the Palaeozoic by a diagram, Fig. i. This is 
intended to show some features of a vertical section at the fortieth 
parallel. The left extremity of the diagram is supposed to be in 
the longitude of the Pacific coast and the positions occupied by 
the Sierra Nevada, by longitude 117° and by the Wahsatch range 
are noted. The diagram does not pretend to exhibit the con¬ 
figuration of the land surface, but merely indicates the limits be¬ 
tween the land and the sea. 
At the close of the Palaeozoic a great change took place in the 
Pacific slope. Western Nevada with portions of Oregon sank 
below sea level, while a large part of the sea bed to the eastward 
rose. The newly elevated area embraced the eastern portion of 
