The highest portions of our Ulue mountains, as the Eagle Creek or WaHowa mountains and the Elkhorn mountains, stand out as islands of limestone or marble and slate completely surrounded and partially submerged by those great lava flows. As Lindgren says of them: "The lower water courses became filled with basalt, damning its headwaters and creating lakes. The sharp slopes became sloping plateaus, and finally the Blue mountains stood like islands in a basaltic sea." The great lava flows through which the Des Chutes has worn its way, have been vividly described by Professor Condon in The Two Islands. While Rus- sell, of the United States Geological Survey, gives us a most interesting picture of Stein mountain with its thousands of feet of old basaltic lava. Here it can be studied in vertical sections, by reason of a fault which has left the highest part of this mountain block tilted up 5,000 feet above the Alvord valley at its steep eastern face.
Some of this lava flood in the northwest may have taken place as early as the Eocene age and some in much later times, but the greater part is believed to be the work of the Middle Miocene.
UPPER MIOCENE AGE
When this period of vnlcanism had passed and sufficient time had elapsed for the making of new soil by the crumbling and disintegration of volcanic rock; when shallow lakes had formed in the depressions above the lava flood, and herb- age and forests had again covered the vast expanse of dreary lava beds ; when at last mammals were again at home in eastern Oregon, we find that time had wrought mau.v changes. We miss the herds of oreodons for they had become al- most extinct. Even the fierce elotherium which was so well equipped for the struggle of life had disappeared. The rhinoceros, so common on the older Ore- gon lake shores, was seen no more. The three-toed horses were more numerous than before, but they wei-e quite different from the earlier horses, being now as large as an average Shetland pony and in every way more like the modern horse.
There were several new types in the camel family. And Dr. Merriam reports the first of Oregon mastodons as found in the Upper Miocene rocks. The stream of life had not diminished, but on the contrary, at no period in geological history of the northwest has it seemed so rich and full.
During the Upper Miocene the forests of Oregon and Wa.shington seemed to have reached the climax of their glory. In the John Day valley alone Knowlton, the Paleobotanist, reports eighty different forms, including the fig tree, magnolia, acacia, butternut, walnut, hiekorynut, birch, alder, bald cypress, Japanese cedar, three species of the sequoia family, to which the California big tree and redwood belong, seven species of oak, eight of maple, nine of willow, two of elm, three of sycamore, four of liquid-amber, the persimmon, horse chestnut, laurel and the maiden hair tree, or Japanese gingko.
Dr. Diller, in speaking of northern California during the Upper Miocene epoch, says: "No doubt the Sierra Nevada existed at that time, but its height was very low, at least in the northern part as compared with its present altitude. " The same might be said of the Cascade mountains of Oregon, so that the warm moisture-laden winds swept unhindered over this whole fertile region of the
