38 GEOLOGY KLAMATH BASINS. 



any cause now operating, and it is quite certain that the surface of the surrounding country- 

 like all that which we traversed west of the Cascade mountains has never been swept hy a 

 drift current. I can only explain it by connecting it with the presence of a much larger 

 quantity of water in this basin at a former period than is found here now. 



In that portion of the Klamath basin through whicti Lost river flows, the same sandstone is 

 found interstratified with infusorial marls, which are fine and white. At the &quot; Natural Bridge&quot; 

 these strata have been thrown up by a fault, and form a dam across the stream, where it is 

 forded. The sandstone here contains black scoria in rounded masses, frequently as large as an 

 egg. In this respect, as well as in texture, it resembles a sandstone forming part of the series 

 of tufaceous marls, described in Chapter I, as occurring on the south shore of the San Pablo 

 bay. Here, as there, the greater part of the material being undoubtedly of volcanic origin, 

 consisting of ashes, comminuted pumice, mingled with masses of scoria, all of which have been 

 thrown into water and stratified by deposition. 



I may say, in this connexion, that I obtained from Mt. Hood, in Oregon, volcanic ashes which 

 had been recently thrown out, which would form precisely similar strata, if similarly treated. 

 From Lost river, these infusorial marls underlying the surface of a nearly level plain, extend to 

 and artially surround Lower Klamath lake, reaching as far north as the southern end of Upper 

 Klamath lake. On the shores of Rhett lake, and several localities on the plain, which I have 

 mentioned, the surface is covered with a white efflorescence resembling snow. It is doubtless 

 derived, in a great degree, from the marl beds, which usually contain a notable quantity of 

 soluble salts. Specimens of this efflorescence was remitted to Dr. J. D. Easter for analysis, 

 upon which he has rendered the following report : 



&quot;A white saline efflorescence from Rhett lake, Oregon. The salt, freed by solution from earthy 

 and vegetable matter, consisted of sulphates of soda and magnesia, with a considerable proportion 

 of chloride of sodium. A quantitative analysis was begun, but the vessel containing the solu 

 tion was broken during my absence from the laboratory, and no more of the salts remained. 

 The efflorescence is similar to a large number of specimens which I have analyzed from Cali 

 fornia and New Mexico.&quot; 



Across the south end of Upper Klamath lake a low ridge of trap runs, by which its waters 

 are considerably raised above the plain surrounding Lower Klamath lake. On the flanks of the 

 hills which compose this barrier I found the infusorial marls, here highly metamorphosed, some 

 of the % specimens approaching jasper in appearance. The hills bordering the lake near its 

 southern end are composed of soft pulverulent sandstone, similar to that found on the shore 

 of Rhett lake, and, like that, composed of thick beds of trap. 



The hills bordering Upper Klamath lake are high and bold on either side : on the west, 

 rising in successive grades until they join the Cascades, here crowned by the lofty and sym 

 metrical cone of Mount Pitt ; on the east, a succession of trap ranges, having a trend nearly 

 northwest and southeast, terminate in bold headlands which project into the lake and form its 

 shore. These ranges rise to an altitude of twelve to fifteen hundred feet, with valleys of corre 

 sponding depth. They are composed of dark vesicular trap, in some places scoriaceous. The 

 most northerly of these interrupted ranges, along the northern base of which Klamath rirer 

 flows for several miles, is, in a great degree, composed of volcanic breccia, the enclosed frag 

 ments ranging in size from two to six or eight inches in diameter. 



At the junction of the east branch of Klamath river with the main stream, for some distance 

 along the base of the ridge of which I have spoken, a stratum of infusorial marls is exposed, 



