Ch. II.] VARIETIES OF CORNISH GRANITE. 17 



sometimes this rock becomes quartzose, by the gradual loss 

 of the felspar, analogous to the perfect shorl-rock, and in 

 this state it forms the only protruding masses ; for the granitic 

 kinds are so prone to decay, that they are perfectly disin- 

 tegrated for more than twenty feet beneath the surface. This 

 quartzose protogine is, however, more commonly seen as loose 

 boulders on the hills ; and although now seldom found, they 

 were probably more abundant formerly, as this stone enters 

 pretty largely into the construction of churches and other 

 ancient buildings in the neighbourhood. 



It has already been stated, that the granular mixture of the 

 true granite sometimes becomes so minute, that its consti- 

 tuents can scarcely be discerned by the naked eye. This 

 variety frequently passes into such a fine granular homo- 

 geneous rock, that, even with the magnifying lens, we cannot 

 detect the usual granitic minerals : it appears, indeed, to have 

 passed, by the intimate blending of the quartz and felspar, 

 into a variety of compact felspar, to which the name of eurite 

 may be appropriately applied. This substance, however, is 

 seldom perfectly pure, but forms a basis in which small granules 

 of quartz and minute scales of mica are imbedded. It some- 

 times becomes porphyritic, by the presence of distinct crystals 

 of felspar ; in some places it also contains shorl or hornblende ; 

 and it not unfrequently happens that, towards the centre of 

 a bed of eurite (by the increased size of the concretions of 

 quartz, mica, and felspar), the basis disappears, and the rock 

 becomes a perfect fine-grained granite. 



This euritic suite of granitic rocks prevails in certain parts 

 of Cornwall, while in other parts a similar series occurs, only 

 the basis, instead of being fine, granular, and rather soft, as 

 in the eurite, is a hard compact felspar ; so that, although 

 the composition of these rocks appears to be the same, their 

 appearance is very dissimilar. It is proposed to call this 

 genus felsparite, in order to distinguish it from the other 

 granitic rocks. The species of felsparite arise from the nature 

 and disposition of various minerals in the basis of this genus, 



