109 
November 28, 1870. 
Prof. B. N. Martin, Vice President, in the chair. Fifteen 
persons present. 
The following paper was read, 
On the Formation of Deposits of Fresh-Water Diatomacez, 
By Pror. A. M. Epwarps. 
The presentation at a recent meeting of this Society, of a 
specimen of a material which is commonly known as 
“Infusorial earth,” and the discussion arising therefrom, has 
persuaded me that a somewhat detailed account of what is 
known concerning this kind of substance, its mode of forma- 
tion and geological relations, would prove of interest to my 
fellow members. I, therefore, propose to give in this paper, 
a brief resumée of the results of very extended examinations 
made in this field and extending over the last eighteen or 
twenty years. At the same time, I shall endeavor to place 
the subject in such a light, that hereafter the true characters 
of these deposits, shall be understood and not misrepresent- 
ed, as is unfortunately almost always the case, in published 
works treating either of geology, microscopy or general 
natural history. At the outset, it would seem hardly 
necessary to describe the characteristics of the Diatomacez, 
the organisms which make up the mass of these deposits, and 
yet it will be as well to say something on this point so as to 
assure the understanding of what I have to say hereafter. 
The Diatomacez, then, are extremely minute organisms 
which are most commonly classed among the alew or 
eryptogamous aquatic vegetables, and live in both fresh and 
salt water submerged and, for the most part, adherent to 
sticks, stones and other similar substances as well as larger 
plants. They are considered to be unicellular and have 
skeletons which consist of usually two sections, which shut 
together like the upper and lower portions of a box connected 
PROC. LYC. NAT. HIST. N. Y.—VOL. L 8 
