280 Dr. FiTTON on the Geology^ t^c. 



Cork Institution, from whom the specimens that I have seen were 

 obtained, informs me, that it was found at a small distance from the 

 surface, near the base of a hill composed of a flinty slate, and that he 

 has seen it adhering to a piece of rock of that description. But it 

 has occurred principally detached in the form of globular nodules, 

 irregularly grouped together, and of various sizes, the longest about 

 an inch in diameter, externally coated with a yellowish brown 

 earthy crust, and within composed of radiating crystalline spiculsc, the 

 characters of which agree very nearly with those of the wavellite from 

 Devonshire, described by Mr. Davy; indeed some of the specimens 

 from the county of Cork, are scarcely to be distinguished from some 

 of those obtained at that place. 



The most distinct specimen that I have seen was a nodule about 

 three-fourths of an inch in diameter, in part affected by decomposi- 

 tion and containing some small spongy cavities. On its external 

 surface indistinct dihedral terminations of the crystalline shoots are 

 discernible ; and internally, where it is not decomposed, its lustre is 

 higher and more glossy than is common in the Devonshire fossil. 

 The specific gravity of that part of it, which was vety pure and 

 nearly transparent, was 2.34. 



The nodules are in some instances decomposed throughout, the 

 spiculse having lost their lustre, acquire a dull grey or brownish colour, 

 and become much softer than when unchanged ; and Mr. Hincks has 

 seen some of them altogether in the state of clay, apparently from the 

 effect of decomposition. 



It would appear that the fluoric acid, of which Mr. Davy has 

 ascertained the presence in the w^avellite from Devonshire, exists 

 also in that from Cork ; for glass is corroded by heating upon it, in a 

 drop of sulphuric acid, a fragment of the mineral from either of those 

 places. 



