320 PROCEEDINGS OF THE CALIFORNIA 



The material of which this deposit is made up is exceedingly fine-grained, 

 seemingly an impalpable powder, usually perfectly white and more or less dis- 

 tinctly stratified. It is extremely light, and resembles commercial magnesia 

 more than anything else. In its geological position, it is found underlying the 

 basaltic masses, or the products of the last great eruptive action of the Sierra 

 Nevada. It is often associated with, or intercalated among beds of gravel, 

 fine or coarse-grained sandstone and shales, and bears the evident marks of being 

 a sedimentary deposit made along the sides of a gently-descending broad valley, 

 or lake-like expansion of a valley. This is its character in the Sierra Nevada ; 

 but as we go north and northeast, and come ou to the great volcanic table lands 

 of Northern California and Southern and Eastern Oregon, we find the thick- 

 ness of the deposits of this kind of material increasing, and the area occupied 

 by them more considerable. The following localities are especially worthy of 

 notice : North of Virginia City, Nevada ; Surprise Valley ; Pit River, near 

 mouth of Canoe Creek ; Klamath Basin, or in the vicinity of Wright, Rhett 

 and Klamath Lakes ; the Des Chutes Basin. 



Of all the localities, the last mentioned would seem to be the most 

 remarkable for the extent and thickness of the deposits in question. It 

 was from here that the first specimens examined by Ehrenberg, in 1849, 

 were brought by Fremont, who represented the deposit as 500 feet thick. 

 This region has since been examined by Dr. Newberry, who describes the 

 canons of the tributaries of the Des Chutes as in places 2,000 feet deep, 

 the plateaux between which canons are covered by basaltic lava, and 

 this is seen, in the magnificent sections thus presented, to rest on a thickness of 

 hundreds of feet of tufaceous strata interstratified with a variety of beds of 

 volcanic conglomerates, pumice sand, ashes, etc. Dr. Newberry speaks of tufa- 

 ceous strata 1,200 feet in thickness, in the canon near the mouth of the Mpto- 

 lyas River. 



The white material, of which some of the more prominent localities have 

 been indicated above, and which is well known to explorers under so many 

 names, as already mentioned, is in reality chiefly of a silicious character, and 

 made up, to a large extent, of organic bodies of microscopic dimensions, infu- 

 soria, or Diatomacea. This fact was first recognized in the case of the specimens 

 collected by Fremont on the Des Chutes River, and examined by Bailey and 

 Ehrenberg. Specimens collected by Dr. Newberry, on the Pacific Railroad 

 Survey, were also examined by Professor Bailey, but I am not aware that any 

 detailed description of the results was ever published. 



Among the collection of the Geological Survey are a large number of speci- 

 mens of the white infusorial deposit, underlying the lava at various localities. 

 Of these a preliminary examination has been made by Professor Brewer, and a 

 large supply of material is now iu the hands of Mr. A. M. Edwards, of New 

 York, for a detailed examination and report. The fact has been already well 

 demonstrated that all or nearly all these fine, white, light masses are made up, 

 to a large extent, of the silicious remains of the diatomaccce, and in all cases 

 of forms peculiar to fresh water. The geological position of these beds is ex- 

 tremely recent. They extend from the latter portion of the Pliocene into the 



