CHAPTER XIII.
THE GEOLOGICAL FORMATION OF OREGON AND WASHINGTON.
According to Mr. Condon, formerly State geologist, the Rocky Mountains once formed the western breakwater of the continent, as the Coast Mountains now do. They were forced up by the subsidence of the ocean bottom, and the consequent upfolding of the earth's crust. The upheaval occurred near the shore-line, but left a narrow strip of the old sea-bed east of the Rocky Range; enough to prove that the upheavel occurred in the Cretaceous period. A large body of salt water was thus isolated, which gradually, by natural drainage, became brackish only, and finally quite fresh. This change is also proved by the nature of the deposits.
After a long interval of quiet, another upheaval took place, occasioned, like the first, by a subsidence of the ocean-bed. At this second folding of the earth's crust, the Cascades and Blue Mountains were forced up, and once more a large body of seawater was divided off from the ocean, to form great salt lakes, which gradually became fresh. The Blue Mountains formed an island, separating the northern portion of these waters from the southern, which were drained respectively by the Columbia and the Colorado Rivers; but not until by deposits of various character did the bottoms of these basins become sufficiently elevated.
In like manner, the later upheaval of the Coast Range caused to be enclosed between these mountains and the Cascade Range another immense body of water, which became fresh in time like the older lakes, and with the gradual elevation of the sedimentary deposits was finally drained off like them. That the dates of the formation of these lakes were widely separated is evident from the fossils of each, which indicate the geologic period to which they belonged—the deposits of the Wallamet Yalley being the most recent.
In the mean time vegetable and animal life flourished along the shores of these inland seas or lakes. There are canons in East Oregon fifteen hundred feet in depth, whose walls present a
