TO GEOLOGY. 995 
families Lymneana and Peristomiana, analagous to the 
species now inhabiting the adjacent waters, line and form 
the shores of the whole circumference of the lake, to the 
depth and breadth of many fathoms. Not having visited 
this interesting lake myself, 1 repeat what has been com- 
municated to me by intelligent, scientific friends, who 
have examined it, and on whose report the most implicit 
reliance may be placed. Such is the quantity of bleached 
shells now remaining there, that thousands of tons of these 
small species, in a state of perfect whiteness, could be ob- 
tained, if any useful purpose required the removal of them. 
For agricultural purposes, this mass might prove of 
great utility. One friend, I remember, mentioned to me, 
that he had obtained a sharp pointed pole, which he 
inserted ten or twelve feet perpendicularly into the mass, 
on the shore, near to the edge of the water, without its 
having passed through it. As far as can be ascertained, 
this mass seems to form the whole basin of the lake, and 
it may, at some future, and, perhaps, not far distant period, 
form a tufaceous lacustrine deposit, similar to that at 
Syracuse. 
These very circumscribed deposits are of no very great 
geological importance, but they indicate to us, in a small 
way, the processes by which nature has formed those lacus- 
trine deposits which are of a wider extent, of more ancient 
origin, and which compose part of nearly all the groups 
which Mr Lyell divides into Metamorphic, Plutonic, Vol- 
canic, Freshwater, Marine and Alluvial.* 
é * Principles of Geology, vol. 3, pp. 374, 386. 
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