OF PENTLAND HILLS. 619 



ingredient in their porcelain. The quantity of 

 iron which our felspar contains, renders it unfit 

 for the finer kinds of porcelain. 



In several of the lateral valleys in the Pentland 

 range, there occurs a greyish and yellowish -white 

 coloured clay stone *, which agrees in many of its 

 characters with compact felspar. This mineral 

 should be analysed, as there is a probability of its 

 containing the same constituent parts as felspar, 

 with the exception of the iron ; and if so, it would 

 answer for the finest kinds of porcelain. 



* This porphyroidy or porphyritic claystone, bears a 

 striking resemblance to the porphyroid of Auvergne, 

 which Fnujas de bt Fond, Delametherie, Haiiy, Cordier, 

 and Von Bnch, consider as a volcanic product. 



