of Devonshire and Coriiwall. 125 



Stephen's Church, and v/hlch is about six hundred and thirty-five 

 feet above the level of the sea. 



From Step-aside, we enter upon a mountain-plain of decomposed 

 granite in the state of kaolin, which is famous for the porcelain earth 

 it affords, and which is sent to Worcestershire. This plain is some 

 miles in extent, and belongs to the southern boundary of the chain. 

 One of the most elevated points of it, and which is in the neighbour- 

 hood of the principal quarry of the porcelain earth (China pit) is eight 

 hundred and thirty feet above the level of the sea. This granite, the 

 felspar of which forms two-thirds of the mass, appeared to me to be 

 less decomposed near the borders of the plain, than in the central 

 part. In this last place it has rather the appearance of a porphyry 

 with a pulverulent base, of a whitish colour, in which crystals of 

 quartz, and some plates of mica, are loosely included. It is used in 

 this rough state in the manufacture of porcelain, in the same 

 manner as the Chinese make use of petuntze, by mixing it in 

 certain proportions with the porcelain earth that is obtained by 

 washing and frequent precipitations. Crystals of a compact and 

 earthy felspar are occasionally met with in this decomposed granite, 

 of a much larger size than usual. We also find here another rock, the 

 geological position of which is very interesting ; I mean the schorl 

 rock^^ a binary compound of schorl and quartz, in which the first 

 considerably predominates. We find masses of it of all sizes, gene- 

 rally of a rounded shape, and coated on the surface with the porce- 

 lain earth. There are also large blocks of it in the bed of the Fal, 



* " The schorl rock of CornwiU is probaWy very intimately connected with topaz 

 " rock.'' Jameson's Elements of Geognosy, 



The same author adds in a note — " The geognostic relations and characters of schorl- 

 *' rock are not well ascertained, therefore 1 have declined saying any thing regarding ii 

 *< in the text." 



