150 ASSOCIATIONS OF [Ch. VIII. 



a fine, compact, granular, siliceous sandstone, of this descrip- 

 tion is the largest vein, which is more than five feet thick ; 

 others, again, are porphyritic, containing crystals of felspar, 

 of tourmaline, or of mica,* and lastly, some of the veins 

 abound in felspar, and resemble veins of compact felspar 

 rather than granite. No where could any connection be 

 traced between the veins and the great neighbouring granitic 

 mass; and most of the veins, even the smallest, appeared 

 insulated. No small masses of granite were observed included 

 in the killas, or of the killas in the great mass of granite : but 

 small portions of killas, similar to the contiguous rock, were 

 not uncommon occurrences in the granite-veins. A vein of 

 quartz occurs near the lode of Little Bounds, in killas, on the 

 sea-shore: it is three or four inches broad, has numerous 

 branches, contains very good crystals of felspar, and some 

 coarse quartz crystals with plates of mica ; and in one place, 

 by a happy mixture of these substances, a compound is 

 formed, which has very much the appearance of common 

 granite, and seems only to differ from it in containing more 

 mica and felspar than usual, and in being softer and less 

 compact.* 



Mr. Carne f has remarked, that at Forth Just and Polladen 

 Cove, the granite, in several places, appears to be insulated 

 in the slate ; but from the relative situation and size of these 

 apparent bunches, he thinks it probable that they belong to 

 different veins, whose continuity at the surface has been either 

 prevented, or broken, by the slate : and he is also of opinion 

 that the large vein of Forth Just, six feet wide, is not a gra- 

 nite vein, but an elvan-course. 



" At Polmear Cove, in Zennor," says Mr. Carne, " the 

 granite veins are as singular and interesting as any in Corn- 

 wall, They are from the smallest possible size to nearly two 

 feet in width : they run in several directions ; some of them 



* Geol. Trans, of Cornwall, vol. i. p. 22. Dr. Davy, on Granite-veins at 

 Forth Just. 



f Geol. Trans, of Cornwall, vol. ii. p. 67. 



