332 GEOLOGICAL SURVEY OF THE TERRITORIES. 



described a portion of the country drained by the Columbia, and have 

 given the facts that lead me to assert that the gorge through which it 

 passes the Cascade Mountains has been excavated by its waters ; and 

 that previous to the cutting down of this barrier these waters accumu- 

 lated to form great fresh-water lakes, which left deposits at an elevation 

 of more than two thousand feet above the present bed of the Columbia. 

 Similar facts were observed in the country drained by the Klamath and 

 Pit Rivers, and all pointed to the same conclusion. 



In all this region I observed certain peculiarities of geological struc- 

 ture that have been remarked by most of those who have traversed the 

 interval between the Sierra Nevada and the Rocky Mountains. In the 

 northern and middle portions of the great table-lands the general surface 

 is somewhat thickly set by short and isolated mountain ranges, which 

 have been denominated the " Lost Mountains." These rise like islands 

 above the level of the plain, and are generally composed of volcanic or 

 metamorphic rocks. The spaces between these mountains are nearly 

 level, desert surfaces, of which the underlying geological structure is 

 often not easily observed. Toward the north and west, however, wher- 

 ever we come upon the tributaries of the Columbia, the Klamath, or 

 Pit Rivers, we find the plateaus more or less cut by these streams and 

 their substructure revealed. 



Here the underlying rocks are nearly horizontal, and consist of a 

 variety of deposits, varying much in color and consistence. Some are 

 coarse volcanic ash, with fragments of pumice and scoria. Others I 

 have in my notes denominated " concrete," as they precisely resemble 

 the old Roman cement and are composed of the same materials. In many 

 localities these strata are as fine and white as chalk, and, though con- 

 taining little or no carbonate of lime, they have been referred to as " chalk- 

 beds" by most travelers who have visited this region. Specimens of this 

 chalk-like material gave me my first hint of the true history of these 

 deposits. These, collected on the head- waters of Pit River, the Klamath, 

 the Des Chutes, Columbia, and elsewhere, were transmitted to Professor 

 Bailey, then our most skilled microscopist, for examination. Almost the 

 last work he did before his untimely death was to report to me the results 

 of his observation on them. This report was as harmonious as it was 

 unexpected. In every one of the chalk-like deposits to which I have 

 referred he found fresh-water diatomacece. 



From the stratification and horizontality of these deposits, I had been 

 fully assured that they were thrown down from great bodies of water 

 that filled the spaces separating the more elevated portions of the interior 

 basin, and here I had evidence that this water was fresh. Since that 

 time a vast amount of evidence has accumulated to confirm the general 

 view then taken of the changes through which the surface of this por- 

 tion of our continent has passed. From Southwestern Idaho and East- 

 ern Oregon I have now received large collections of animal and vege- 

 table fossils of great variety and interest. Of these the plants have 

 been, for the most part, collected by Rev. Thomas Condon, of The Dalles, 

 Oregon, who has exposed himself to great hardship and danger in his 

 several expeditions to the localities in Eastern Oregon where these fos- 

 sils are found. The plants obtained by Mr. Condon are apparently of 

 miocene age, forming twenty to thirty species, nearly all new, and such 

 as represent a forest growth as varied and luxuriant as can be now found 

 on any portion of our continent. 



The animal remains contained in these fresh-water deposits have come 

 mostly from the banks of Castle Creek, in the Owyhee district, Idaho. 

 The specimens I have received were sent me by Mr. J. M. Adams, of 



