CHANGES IN ELEVATION. 669 
chain of the continent was beneath the sea until the cretaceous 
epoch.* The Rocky chain, at this period, was still five thousand 
feet below its present level. Since the tertiary era, the coast on the 
Pacific shore has probably been increased in altitude above the sea at 
least fifteen hundred feet. 
The parallelism of the chains of mountains has been particularly 
considered ; and we have also pointed out, in another place, the pro- 
bable connexion between the depressing of the Pacific Ocean and 
the formation of the great parallel lines of elevation that form the 
western border of North America. Whether these lines commenced 
to form together, or were begun in succession, we cannot now decide. 
Granitic rocks occur in both the summit crest and the Cascade 
Range. The lofty cones of the latter are proof of the great depth and 
extent of the rupturings that marked the commencement or progress 
of this volcanic chain. 
Basaltic eruptions have continued in Oregon to a late period, and 
even now some of the volcanic peaks, as has been stated, still eject 
ashes. ‘These rocks may, in some parts, be of very early age ; on this 
point no definite information was obtained. That ejections took place 
before and during the miocene tertiary period, and have occurred 
since, is beyond doubt; for they occur below the sandstone; and, as 
dikes, they intersect it. The surface basaltic lavas are probably of 
comparatively recent date. ‘Those of the Willammet Falls and John 
Day’s River resemble a recent scoria: this fact, however, is no evi- 
dence, by itself, of modern origin; except so far as it proves that the 
eruptions producing them were subaerial, and therefore must have 
happened since the cretaceous period, when a large part of the eleva- 
tion of the Rocky Mountains took place. 
The vast amount of silicified wood throughout Oregon may be 
readily accounted for, in a region where igneous action has been so 
extensive, and siliceous waters, from submarine eruptions or from 
springs, must have been abundant. The chalcedony and agate of the 
country, which come from the amygdaloidal basalt, have evidently 
had a similar origin. The zeolites of the same rock may have been 
formed in part from similar siliceous waters, or from waters infiltrating 
through the rock, and carrying along some of the decomposed material. 
The deposition of the tertiary sandstone took place along a sea- 
shore, while igneous operations were going on in the same region, and 
* Darwin on South América, 8vo., London, 1846 ; page 238. 
168 
