NOME VIII. KOLLANITK. ] 05 



rived from the siliceous impregnation of several 

 animals, which existed in the primeval waters. 

 He supposes that the pebbles were at first soft 

 nodules of martial clay, or marl, often composed 

 of laminae of different colours ; such, as he says, 

 have been frequently found in the gravel-pits of 

 England, and in large heaps in various parts of 

 Italy. They are afterwards impregnated with 

 siliceous juice, which may be of very recent 

 origin ; for silex is soluble in water, as appears 

 from the analysis of many medical waters of 

 England, not to mention the fountain of Gey- 

 zer in Iceland : and Mr. Davy has shewn that it 

 enters into the composition of the epidermis of 

 many reeds, and even of oats, wheat, barley, and 

 other graminous plants; that of Dutch rush, in 

 particular, seeming to consist entirely of silex. 

 In stacks of burnt hay, there are found porous 

 stones, resembling frits of glass. From these 

 examples it can scarcely be denied that silex 

 may often be produced from decayed vegetables. 

 There may, however, be two formations of pud- 

 ding-stone. The celebrated Fracastorius was 

 the first neptunist, as he was the first who in- 

 ferred fossil shells were not lusus nature, but 

 formed by the primeval waters which covered 

 the earth. But if these shells existed even in the 

 primeval ocean, it would be difficult to assign. 



