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most commonly represented in, and making up the mass 
of the lLacustrine Sedimentary Deposits are Navicula, 
Pinnularia, Stauroneis, Synedra and similar elongated forms, 
the hard, white material is in general found to consist of 
myriads of examples of Orthosira, Cyclotella and similar 
discoid forms. Although our knowledge of the forms of 
these minute organisms, peculiar to different kinds of collec- 
tions of water is rather imperfect, yet we do know that in 
moderately-small ponds and lakes, we find the Naviculzeform 
genera spoken of above, whilst in the larger lakes are to be 
seen growing more particularly the discoid genera like 
Cyclotella. From this fact alone, then, we should be prepared 
to assume that the waters in which the organisms whose re- 
mains make up these deposits, grew at one time, covered 
large tracts of country. And our surmises on this point, are 
confirmed by the reports of explorers who have passed over 
this section of country; that is to say on both sides of the 
Sierra Nevada Mountains, and extending from Puget’s Sound 
to the southernmost border of California. 
I have examined many specimens from this district and on 
account of the mode of occurrence of this material; being 
capped by Lava, Basalt or some volceanically-erupted rock, I 
have designated them Sub-Plutonic. The first specimens of 
such Sub-Plutonic deposits of Diatomaceze which were put 
into the hands of scientists were undoubtedly those brought 
home by Frémont from his expeditions to the Rocky Moun- 
tains in the year 1842, and to Oregon and North California in 
the years 1843-44. The discovery of these, as detailed in 
his report, gives a good idea of this portion of a country and 
is as follows. It must be premised that in that report, what 
is now known as the Des Chutes River, and which is one of 
the tributaries of the Columbia, is called “ Fall River (Riviere 
aux Chutes,”) so, also, he spells Klamath Lake “ Tlamatt.” 
Speaking of the tributaries of the Columbia, he says, (page 200,) 
“These streams are characterized by the narrow and chasm- 
like valleys in which they run, generally sunk a thousand feet 
below the plain. At the verge of this plain, they frequently 
commence in vertical precipices of basaltic rock, and which 
