CHAPTER VII. 



GEOLOGY OF THE COUNTRY BORDERING THE COLUMBIA RIVER. 



Region east of the cascade mountains. — General features apparently similar to those of des chutes basin. — Local geology. — 

 Dalles of the Columbia. — Sedimentary infusorial deposits. — Their fresh water origin. — Their age. — The canon of the 

 Columbia. — General features. — How formed. — Local geology. — Horizontal strata of trap. — Submerged forest. — Cascades 

 formed by slide from mountains.— Conglomerate.— Silicified wood.— Tertiary strata below cascades— Country bordering 

 the lower columbia. — general features. — willamette yalley. — its resemblance to the californian valley. — local 

 geology. — Western slope of the cascade range. — Canon of mckenzie's fork. — Marks of glacial action on mount hood. — 

 Trap, scoria, ashes, etc., from mount hood. — Trap and sandstones of Willamette valley. — Erosion of sandstones. — Lignites 



near st. helens. — terraces. — coast mountains. — sandstones and shales of astoria. fossils.— age of the deposit. — port 



Urford. — Tertiary sandstones, trap.— Gold. 



GENERAL FEATURES. 



The entire region drained by the tributaries of the upper Columbia has apparently so many 

 features common to all its parts, in its geological structure, its climate, its indigenous plants 

 and animals, that it can only be properly studied as a whole. So viewed, it would furnish an 

 interesting subject of investigation in tracing the connexion and community of character of its 

 parts, and deducing from the common phenomena which they exhibit the common causes which 

 have produced them. 



Tbe Des Chutes basin and the banks of tbe Columbia in the immediate vicinity of the Dalles 

 are the only portions of this area which 1 visited, and I should not be warranted in deducing 

 the structure of the whole from so small a part. From published and oral descriptions, how- 

 ever, of the country traversed by the upper Columbia, as well as from specimens received from 

 different localities, I am led to believe that the Des Chutes basin may be considered as a type 

 of the greater part of it ; and that what has been said of the origin of the geological structure 

 exhibited by that portion of the basin of the Columbia which I saw, is equally applicable to at 

 least that part of it which lies north of the Columbia, and immediately east of the Cascade 

 range. 



These mountains have, as we learn from the graphic descriptions of Mr. George Gibbs, (U. 

 S. P. R. R. Explor. & Surveys, vol. II,) much the same character north of the Columbia as in 

 Oregon. Volcanic peaks crown the crest of the chain, which have deluged the country with 

 floods of lava, and thrown out showers of ashes, from which beds of tufa have been formed 

 similar to those of the Des Chutes basin. Specimens from the banks of the Yakima and upper 

 Columbia, which I have received, are undistinguishable from those collected on Psuc-see-que 

 creek. Basin-like areas, enclosed by walls, now cut through by the draining streams, have 

 been described in varying language by all who have visited this region. 



The Columbia drains many basins and traverses many canons before it reaches the great 

 gorge in which it flows through the mountains ; and it came to the herculean task of exca- 

 vating that channel, no novice in the art of stone-cutting, but skilled by a training begun with 

 its birth, in the thousand mountain streamlets which combine to form it. 



