296 
It had been remarked that they could be used as fertil- 
izers and if they contained Lime and soluble Silica they 
could be so used, as both of these substances would be of 
use for growing crops. 
Pror. A. M. Epwarps replied that the present specimen 
was only another example of the extensive Sub-Plutonic 
deposits spreading over our western country, the mode of 
formation of which he had fully described a short time since 
before this society. He had examined the present specimen 
by means of the microscope, and found it to be made up 
entirely of the siliceous remains of fresh water Diatomace ; 
as is the case with all of these deposits. With regard to the 
solubility of the Silica present in these deposits, he would 
remark that several years since, when investigating the mode 
of formation of guano and the role that the siliceous organisms 
therein present played in the act of the fertilization of plants, 
he had made a series of experiments which he would briefly 
allude to. First, it must be remembered, that we have no 
thoroughly reliable chemical analysis of any of these, so-called, 
“Tnfusorial EKarths,” so that we can not say for certain that 
the skeletons of the Diatomacez consist of Silica alone ; 
it may be a Silicate. But he had found that when pure 
water was made to percolate several times through such an 
earth, that the earth lost in weight; something was dissolved. 
At first he thought there might be a soluble Silicate present 
normally, but this idea was negatived by subsequent investi- 
gations and he came to the conclusion that the water on 
evaporation (for it always evaporates even at a point as low 
as 82° F.) formed, with the Nitrogen of the air Ammonia or 
Ammonium, and that a soluble Ammonium Silicate was 
formed. This was the mode in which he supposed the Silica 
was dissolved and appropriated by such plants as the Grasses 
which require Silica for the formation of their tissues. He 
was subsequently pleased to find that Schénbein had demon- 
strated that whenever water evaporated in contact with the 
air that Ammonia is formed. And it had also been shown 
that Siliceous sand and rock is disintegrated and dissolved 
