668 OREGON AND NORTHERN CALIFORNIA. 
light alluvium, though sandy along the shores. A mile and a half to 
two miles back, it is a fertile loam, covered with a luxuriant growth 
of grass. The soil is, however, but five or six inches deep, and les 
upon the white beach-sand. 
Cowhtz Valley—The distinction of upper and lower prairie exists 
in the Cowlitz plains, and the two are similar to those of the Willam- 
met. Mr. Drayton states that the upper prairie is raised forty feet 
above the lower. 
CAUSES OF THE FEATURES OF OREGON AND CHANGES IN ELEVATION. 
The great contrast between the east and west sides of the Rocky 
Mountains has been often mentioned, the one abounding in sandstones, 
with some argillaceous limestones, without volcanoes or volcanic rocks, 
while, on the other side, recent igneous rocks prevail, (basalts, basaltic 
lavas and trachytes,) and the sandstones are comparatively of small 
extent. Granites and allied rocks occur on both sides; they form the 
crest of the Cascade Range in most parts, and also the body of the 
range, with the exception of its conical peaks and their vicinities. 
The sedimentary deposits of the eastern foot, near the Mississippi, and 
south in Texas, are, to a great extent, cretaceous in era; and the same 
rocks, according to recent observations, extend to a height of five 
thousand feet on the eastern slopes, to Fort St. Vrain’s, and also occur 
about Poblazon west of the del Norte, situated six thousand feet above 
the sea. About the summit, the formation, according to some imper- 
fect data, has been considered of the Oolitic age. At the western foot, 
there are tertiary rocks to a height of fifteen hundred feet, and, per- 
haps, two thousand; whether cretaceous deposits occur above, before 
reaching Poblazon, has not been ascertained. 
These observations teach us that the Rocky Mountains were be- 
neath the sea, to a very great extent, till a comparatively recent epoch. 
We cannot say when the crests of the range, the Wind River chain 
and other granitic summits, first arose from the waves ; the period may 
have been very distant. But the Oolitic rocks of the summit, if such is 
their real character, (and there is no probability of their being older,) 
show that till then nearly the whole mountain territory was sub- 
merged. Since that time, the dry land has been extending its limits, 
and increasing in elevation above the water level. The investigations 
in South America prove that there a very large portion of this great 
