GEOLOGY KLAMATH BASINS. 39 



which is white and chalk-like, in all respects resembling that from Pit river and the plains 

 about Lower Klainath lake. A few miles north of this occurs another volcanic ridge, having 

 nearly the same trend with those last mentioned, from which it is separated by the nearly 

 level and, in many places, fertile valley through which Klamath river flows. This ridge is 

 composed partly of dark, compact trap and partly of white and soft pumice, which, in many 

 places, covers the surface, and, in its decomposition, gives rise to a peculiarly light and ash-like 

 soil, upon which nothing seems to flourish but the yellow pine. Through this ridge Klamath 

 river flows in a canon, of which the walls are perpendicular and two hundred feet or more in 

 height. 



North of this ridge is another low and level plain, of which the surface is in many places 

 covered with pumice. Crossing another but lower ridge of similar character, we descend to the 

 shores of Klamath marsh. This lake occupies an area similar in all respects to those below, 

 and like them is formed by the crossing of the general trough in which they all lie, of the 

 transverse trap ranges to which I have alluded. Along the eastern shore these ranges are 

 very conspicuous, several of them running far out into the lake, and throwing its eastern border 

 into a series of long points, alternating with deep bays. 



The pumice is here as marked a feature in the geology of the district as the trap ; covering all 

 the surfaces, and forming a soil into which the feet of our horses sank so deeply as to render 

 any departure from the trail which followed the outline of the shore very disagreeable. At the 

 north end of the lake, a point of metamorphosed slate projects a few feet above the surface, and 

 forms the only exposure of rock of this character seen within many miles of that point. 



The western shore of this lake is formed by a broad prairie scarcely raised above the water 

 level, and doubtless at some seasons submerged. It seemed everywhere underlaid by fragments 

 of pumice, which had apparently been so accurately levelled by the action of the water. This 

 pumice, when pulverized, forms a substance having a striking resemblance to the marls to which 

 I have so often referred, and, aside from the organic structures which they contain, they have 

 doubtless been formed of similar materials. 



The interval separating Klamath lake from the head-waters of the Des Chutes river forms 

 a nearly level plain, covered everywhere with pulverized pumice, and supporting a meagre 

 growth of yellow and spruce pine. Both east and west, ranges of hills are visible from the 

 route which we followed, and at various points masses of black basalt project above the general 

 surface. From the porous nature of the soil, the streams which come down from the mountains 

 at the west are soon absorbed, and we were only enabled to obtain water by digging, at a single 

 point on our journey. At this point, the water seems to have been brought to the surface by a 

 dyke of trap rock which impedes its subterranean flow from the west. 



A precisely similar surface borders the south fork of the Des Chutes to its junction with the 

 main stream which comes down from the Cascade mountains. On the banks of this latter stream 

 are exposed, in various localities, strata of white, chalk-like marls, and light brown, green, and 

 friable sandstone, in all respects identical with those of Pit river and Klamath basins. 



