72 PRESIDENTS ADDRESS—SECTION C. 
pliocene Siwalik beds deposited to a thickness of from 5000 to 
10,000 feet. Then, in the Pleistocene, came another upheaval, 
contorting the pliocene beds and forming the sub-Himalaya ; a 
range which runs along the south-west flank of the central 
Himalaya from the Punjab to Assam, the crests of the two 
ranges being about 125 miles apart. But these plications were 
local, for the pliocene beds on the north-east side, in Thibet, are 
not folded, but have been gently elevated. It is not supposed » 
that the thickness of the Siwaliks shows the true vertical measure 
at any one time, for deposition, disturbance, and erosion went on 
together, so that in no place did they reach anything like 10,000 
feet, from which it follows that rocks at the surface must have 
been greatly disturbed. Notwithstanding the comparative 
rapidity with which the sub-Himalaya were formed, the elevation 
was so slow that it never exceeded the rate at which the rivers 
flowing from the Central Himalaya cut down their beds; for 
they all—the Sutlej, Ganges, Ghogra and others—still run in 
their old valleys right across the crest of the sub-Himalaya. 
In the western United States thick sediments were formed in 
Utah and Nevada from the Cambrian to the Carboniferous 
inclusive, reaching 30,000 feet in the Wahsatch district. At the 
close of the Carboniferous, or during the Permian period, these 
sediments were greatly plicated and elevated in the Basin Region, 
the Wahsatch and Humboldt Ranges being formed. The Colo- 
rado district to the east, in which not more than a thousand feet 
of strata had been deposited, still continued to subside. During 
the Triassic and Jurassic periods general depression took place, 
with especially heavy sedimentation in Nevada, west of the 
Humboldt Range. At the end of the Jurassic these beds were 
contorted and elevated, the Sierra Nevada being formed. <At 
the same time the Basin Region was elevated without folding, 
while Colorado and Utah, east of the Wahsatch, where the 
sediments were still less than 3000 feet, although they had been 
accumulating from the Carboniferous period, still continued to 
sink. In the Cretaceous a general subsidence of the whole 
western continent took place, but the Basin Region was not 
depressed beneath the sea. At the close of the Cretaceous, 
general elevation began. In western Colorado and eastern Utah, 
where subsidence had been continuous since the Carboniferous, 
but only about 4000 feet of strata on an average had been 
deposited, the surface was elevated without plication, except 
locally on the east flanks of the Wahsatch, where the Cretaceous 
alone was 11,000 to 13,000 feet thick. The Uinta Mountains 
also rose some 4000 feet above the rest of the plateau, but their 
rise was so slow that the Green River, which crossed a portion of 
the uplifted area, kept its old channel, and cut down a gorge as 
quickly as the land rose. In central Colorado, where the deposits 
were between 8000 and 9000 feet thick, the Rocky Mountains 
