31 I Recent Fossil Fresh-water deposit, fyc. [No. 148. 



A little to the E. of this, the diamond limestone intervenes between 

 the granite and sandstone, underlying the latter in conformable dip and 

 stratification. 



A spring rising from the foot of a mound of conglomerate, composed 

 of fragments of the sandstone rocks cemented by kunker, marks the 

 site of the fossil bed, which lies in a slight depression above this mound, 

 and considerably out of the reach of the spring in its present state. 

 It is only a few yards in extent, and has evidently been deposited 

 by the spring under former conditions, to which I shall allude present- 

 ly. The imbedding matter is also a kunker, but one of a much harder, 

 compact, and siliceous nature than that at present seen around the 

 margin of the spring, and below the mud at the bottom. Portions of it 

 are sometimes so siliceous, as to give fire with steel and scratch glass ; 

 other portions of the rock contain more lime, are less compact, and 

 effervesce freely with acids. The colour is a light brownish-grey ; 

 fracture varying from flat-conchoidal to earthy. 



The shells imbedded are fresh-water, principally melania, with a 

 few small planorbes, and are all of existing genera. The number of 

 the former is so proportionally great, as to excite surprise in persons 

 who have not studied the segregarious habits of the inhabitants of fresh- 

 water and terrestrial shells. Besides the shells there are impressions 

 and casts of the stems of grasses, reeds, &c. perfectly fossilized by car- 

 bonate of lime. 



The shells afford instructive examples of the various stages of 

 fossilization. Some of their coats have been completely converted into 

 sparry carbonate of lime ; others have been filled with the imbedding 

 paste, which, when the shell is broken off, exhibit a cast with a 

 highly polished exterior. Others again are lined with drusy crystals 

 of quartz ; in some, this siliceous crystallization is just beginning to 

 roughen the surface of the interior, and is hardly perceptible without 

 the aid of a lens ; thus exhibiting interesting examples of the processes 

 by which fissures in rocks are lined and filled up with minerals which 

 we look in vain for in the enclosing walls ; geodes of calcedony and 

 agate, with calc spar and crystals of quartz and zeolite in the midst 

 of calc spar. I have seen a solitary and beautiful pyramidal hexagon of 

 rock crystal, glittering like a diamond in the whitest snow, in a mass of 

 the saccharine marble of Carrara. 



None of the shells have lost their carbonic acid, although they have 



