482 H. J. Biddle — Surface Geology of Southern Oregon. 



has no outlet. But a slight rise in the water of the latter 

 would cause it also to become tributary to the Klamath River, 

 as there is no high ground between. 



There seems to be no doubt that this system of valleys was 

 occupied by a large lake, which has been nearly drained by the 

 cutting down of its outlet. The writer was, however, unable 

 to detect any beach lines which would show the extent and 

 depth of the ancient lake. It is possible that it was so shallow 

 that its waves had little force, and left no trace of their action. 

 But fortunately the sediments in its bed are in places exposed. 

 Lost River, an affluent of Rhett Lake, has cut its channel into 

 the floor of the valley to the depth in places of 40 feet. A 

 bluff on the south side of this stream, about 10 miles southeast 

 of the town of Linkville. shows a good section of the lake beds. 

 They are seen to consist chiefly of a light gray, tine-grained 

 earth, which at first sight might be taken for chalk. Inter- 

 stratified with this are occasional layers, but a few inches thick, 

 of sand and pebbles with a ferruginous cement. 



When the earth forming the mass of these deposits is exam- 

 ined under the microscope it is seen to consist wholly of infu- 

 sorial remains. It is homogeneous and of exceedingly fine 

 texture ; compact enough to form steep bluffs, but in small 

 lumps easily crushed between the fingers. It is so light as to 

 float for a moment in water, and adheres slightly to the tongue. 

 The strata dip about northeast, or toward the mountains, at an 

 angle of 12°. This dip may be due to deposition in inclined 

 layers ; but in that case one would expect to find the slope in 

 the opposite direction, or toward the middle of the valley. 

 Without more extended observations it can not, however, be 

 maintained that a tilting of these beds has taken place. At 

 the top of the bluff they are seen to be overlaid by a horizontal 

 layer of gravel, containing rounded lumps of the infusorial earth. 



A system of joints extends through the beds in a plane 

 about parallel to the strike and at right angles to the dip. For 

 a considerable distance the channel of Lost River lies in the 

 infusorial beds, and wherever exposed the jointing is a notice- 

 able feature. The same material may be traced for about 10 

 miles along the northeast edge of the basin in which Linkville 

 lies ; the total extent of the deposit is yet to be determined. 



Mr. J. S. Diller, of the IT. S. Geological Survey, has called 

 attention* to similar infusorial deposits on Pit River and the 

 lower courses of the Klamath. They occur, as in this case, in 

 the beds of extinct lakes. The writer desires to express his 

 obligation to Mr. Rnssell, of the U. S. Geological Survey, for his 

 kind assistance and advice ; to Dr. Chatard, of the Survey, for 

 his analysis quoted ; and to Mr. Merrill, of the U. S. National 

 Museum, for the microscopic determination of volcanic dust. 

 * U. S. G. S. Mineral Resources, 1886, p. 588. 



