670 OREGON AND NORTHERN CALIFORNIA. 
the shales, as the fossils show, were formed over the flats that border 
a sea-shore. The material of the sandstone is, however, in general 
purely granitic, except in the neighbourhood of the volcanic regions, 
where it varies to a tufa and conglomerate. These deposits indicate 
an elevation, as we have said, of at least fifteen hundred feet since 
the upper layers were formed. 
The sandstone and shale have been denuded on a vast scale. 
Although the rocks are nearly or quite horizontal, wherever examined, 
there are no plains in the coast section excepting those of alluvial 
origin. ‘The sandstone has been excavated till the country has be- 
come a region of hills and valleys and alluvial flats. Some of the 
hills rise a thousand feet above the lower prairies, affording thus some 
measure of the extent of the denudation. ‘These are the effects of 
water, aided, probably, by the fractures attending the igneous opera- 
tions of the land. 
The elevation of the Rocky Mountains, whenever it took place, left 
here and there a depression filled with salt water, and the great lake 
Timpanogos, one hundred miles long, appears to be of this character. 
Others that may have existed were drained off and rendered fresh. 
Much salt, however, impregnates the sandy plains, both about the 
summits of the chain, and upon the country below, especially over 
the great semi-desert of California, a region mostly shut off from the 
sea, except in the direction of the Colorado. Indeed, no part of the 
territory seems to be wholly exempt from these saline efflorescences, ex- 
cept the forest region of the shore. Lieutenant Johnson observed salt 
pools in the Grande Coulée, and specimens of salt were brought by him 
from the vicinity of the Spokane. I met with incrustations on the 
Clammat prairie, and patches of Salsola were not uncommon. They 
occur also near the Bay of San Francisco; and near the Caquines 
Straits there is a copious stream of salt water. ‘This prevalence of 
salt may be viewed only as an indication that the country has been 
beneath the ocean. Its continuance in the soil is favoured by the 
comparative dryness of the climate, especially in the upper country. 
Evidence of Change of Level in the River Terraces.—Another epoch 
in the geological history of Oregon is indicated by the river terraces. 
These terraces, as the facts detailed show, occur over a wide extent 
of country. We have traced them from the Cowlitz to the mouth of 
the Sacramento, and along many of the smaller streams, as well as the 
rivers. The following table presents a review of the facts, showing 
their height above the bottom-land of the rivers: 
