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known up to the present time. After a time, however, speci- 
mens came into my hands which were procured from the 
bottoms of existing ponds, and these, besides consisting for 
the most part of little else than Silica, and being of an almost 
pure white color, had no Peat overlying them. Hence, of 
course, I saw the inapplicability of the term “ Sub-Peat” to 
such deposits, and for them I have coined a new name which 
I consider more appropriate, and at the same time indicating 
their usual origin, and including all deposits of fresh-water 
Diatomaceous remains, with the exception of certain peculiar 
layers to be hereafter described. This new name is Lacus- 
trine Sedimentary. Of course the Sub-Peat then become a 
variety of these. 
Deposits of this character are extremely common in this 
country, as well as elsewhere, and it will be at once seen that, 
although any one of them might be of great thickness, yet 
it does not necessarily follow that'it had been forming for any 
very great number of years, and geologists or others are not 
warranted from observance of this one fact of thickness, in 
supposing that a great length of time has intervened during 
its deposition. Thus, some years since I examined one of 
these Lacustrine Sedimentary Deposits, at a spot near the 
town of East Stoughton, in Massachusetts, which was fully 
twelve feet thick, but only covered a few feet of surface, 
which circumstance was due to the occurrence of a dam 
across the course of a stream which arrested its progress, and 
formed asmall deep pond, into which all of the Diatomacez 
which grew for some considerable distance up-stream drained, 
and dieing accumulated as a light grey-colored powder. I 
have received specimens of similar material from many points 
in this country, so that about one hundred have been ex- 
amined. 
The first recorded discovery of a Lacustrine Sedimentary 
deposit of Diatomaces in this country is found in Silliman’s 
Journal, 1839, Vol. XXV. page 118, in an article “On Fossil 
Tnfusoria, discovered in Peat-earth, at West Point, N. Y., 
with some notices of American species of Diatome; by 
J. W. Bailey.” Of this I have a small portion given me by 
