GEOLOGY-KLAMATH BASINS, 
39 
which is white and chalk-like, in all respects resembling that from Pit river and the plains 
about Lower Klamath 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, w r e 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. 
