49 
scopical department of the geological survey of that state, 
now being prosecuted under the superintendence of Prof. C. 
H. Hitchcock. A very extensive Lacustrine Sedimentary 
deposit of the pulverulent kind, and almost white in tint, has 
been discovered on the shores of Lake Umbagog, in New 
Hampshire, and there were indications that it extends beneath 
the waters of the lake, perhaps over the whole bottom. 
These deposits are of interest, geologically and microscopi- 
cally, but at the same time commercially, as they have been — 
used to some extent, not only as polishing powders, but as a’ 
source of very finely divided silica, of which the skeletons of 
the Diatomacez they contain are made up, for the manufac- 
ture of soluble Silicates, or “Soluble glass” as it has been 
called, which is now aconsiderable article of trade. Although 
existing for the most part, in strata of no very great thick- 
ness, or usually covering no more than a few acres of ground, 
yet, as the number of localities from which they have already 
been procured in the Atlantic states is over a hundred, the 
supply for commercial purposes is amply sufficient, without 
having to draw upon the vast tracts covered by the lake de- 
posits of the Pacific coast, or the marine strata of California 
and Virginia. In a forthcoming volume of the Report on the 
Geology of California, the whole subject of these deposits, 
their mode of formation, with descriptions and figures of the 
organisms found in them, will be published, when will be 
cleared up several points of interest with regard to them. 
They must not be confounded as they often are, with the 
marine strata containing the remains of Diatomacez, which 
occur in various parts of the world, and of which I have 
already spoken. That constituting the major part of the 
Coast Range of Mountains running down our Pacific Coast 
through California, is now undergoing investigation, and the 
results arrived at, will be shortly made public. It is known 
as the “Bituminous Shale,” as it is associated with the 
Bitumen of the Pacific Coast, and there, and elsewhere, it has 
been proved to be of Miocene Tertiary origin. The deposits 
containing the remains of fresh-water Diatomacezx, are evi- 
