Ch. II.] QUARTZOSE VARIETIES. 1 9 



granitic aspect, that the rock is undoubtedly entitled to the 

 term quartzose; as at St. Michael's Mount, at Kerris in 

 Paul, and elsewhere. In some cases, however, the felspar 

 gradually disappears ; so that the rock consists only of quartz 

 and mica (the latter, in some parts, bearing no inconsiderable 

 proportion to the quartz), and has a perfectly granular cha- 

 racter, like the hyalomicte of the French, the greizen of the 

 Germans. One notable example of this occurs near Pen- 

 zance, at Ludgvan : it has furnished an excellent building 

 material, which is very common in the old houses of the town ; 

 but, unfortunately, the place whence it was obtained is no 

 longer exposed to view. Its quartz is grey, and rather large- 

 grained ; its mica abundant, in small silvery scales. 



Those varieties in which the mica is more sparing, and 

 more intimately blended with the quartz, may be found on 

 most of the elevated hills ; more particularly at Roughtor, 

 and Kitt Hill. 



In like manner, the shorlaceous granites of the central 

 and Land's End districts abound in quartzose varieties of 

 this rock. When the felspar is wanting, shorl-rock, the equiva- 

 lent of the micaceous hyalomicte, makes its appearance ; and 

 the shorl-rock is either granular or compact, according to the 

 mode in which the component minerals are aggregated. The 

 compact, either simply of a dark colour, or striped with 

 quartz, is the most prevalent, and forms large courses, layers, 

 or veins in the granite. 



The talcose granite, or protogine, also possesses its 

 quartzose varieties under similar circumstances as the true 

 or micaceous granite, and more particularly that kind 

 which results from the disappearance of the felspar; and is 

 a granular compound, of a greenish colour. It is common 

 in the china-stone quarries in the central district, where, 

 however, it is generally associated with shorl ; and it projects 

 on the side of Tregonning Hill, in the form of tors, or per- 

 haps, rather, of boulders or transported masses. It is well 

 adapted for building, like the Ludgvan stone, cleaving well, 



c 2 



