380 Oil the Geological Structure 



6. Hnllowspar, Jameson — (Made, Haiiy). Very di- 

 stinct specimens of this mineral have been found bv Mr. 

 Davy at Aghavanagh in the county of Wicklow ; and I 

 have observed it at Baltlnglass-hill, within a few miles of 

 that place. 



From some passages among the papers of Mr, Stephens, 

 it appears thai he had found reason to suppose that there 

 existed a connection between the species andulusite and 

 made ; although the specimens which he had seen, were 

 not such as to enable him lo decide on the precise nature, 

 of their relation to each other. The a])pcarances of several 

 specimens of the latter mineral, whicli 1 have lately had an 

 opportunity of examining, tend to confirm tliis opinion ; and 

 even induce me to suspect iliat the crystalline part of that 

 curious substance, is in reality the same with andalusite. 

 In one of these especially, a very fine specimen of made 

 from Brilanny in the possession of Mr. L. Horner, that 

 part of the complex crystal, which is usually of a whitish or 

 yellowish hue, has in several places the reddish colour, as 

 well as the lamellar fracture, lustre, and other characters of 

 andalusite; and like that substance also, is infusible before 

 the blowpipe, becoming while and nearly opake : and it is 

 further remarkable, that in this specimen, as in \.\w^-c al- 

 ready mentioned from Douce-mountain, the crystalline 

 matter is in some places invested with a coating of a talc- 

 Jike substance : which is the case likewise, although less 

 distinctly, with several of the specimens of andalusite that 

 1 have seen, from other countries. 



The following substances have been found at places not 

 included within the district, to which the preceding part 

 of this paper relates : but they may perhaps be subjoined 

 without impropriety, as they have hitherto been rare, and 

 are in other respects deserving of notice. 



7. Pitchdone. This mineral has been found in a vein 

 traversing granite, in the vicinity of Newrv, in the county 

 of Down ; where it presents the following characters, for 

 part of the description of which, I am indebted to Mr. 

 Jameson of Edinburgh : — 



Its colour is intermediate between mountain and leek 

 green. 



Tt is massive. 



Fracture small and not very perfect conchoidal : 



Internal lustre vitreous, and shining. 



]t exhibits lamellar distinct concretions : the plates being 



from 



