TO GEOLOGY. 225 



families Lymnceana 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.* 



* Principles of Geology, vol. 3, pp. 374, 386. 

 2D 



