188 Rev. J.J.Conybeareonihe [March, 



ascertain how far this is the case in veins which traverse 

 granite. 



At Kit Hill above-mentioned, at Carglaise, and at some other 

 places, we were assured by miners apparently of competent 

 information, that the granite did in some places overlie the 

 killas. In these instances, it is possible that granitic dykes may 

 have been mistaken for the central mass, or that our informants 

 might have been misled by some of those deceptive appearances 

 which are familiar to most geologists. Mr. Taylor, in his excel- 

 lent Survey of the Mining District, mentions an analogous fact, 

 and his observation is too important to be omitted. " In Dol- 

 coath and five other mines situate near the junction, the strata 

 of oranite and killas appear alternately overlying each other, the 

 divisions between them being at various inclinations ;* but suffi- 

 cient information cannot be obtained to state with accuracy the 

 particulars. "+ 



On the subject of granitic veins, my memoranda afford 

 nothing which can add to the copious and masterly observations 

 of Mr. Sedgwick. I may mention, however, that the country 

 near the junctions of Cam -brae, of Kit Hill, of the upper part of 

 the river Okement, and of some other spots of the same cha- 

 racter,! will afford the collector hand specimens well calculated 

 to illustrate on a small scale many of the phenomena which pre- 

 sent themselves so fully and magnificently at the cliffs of Tre- 

 wavas and Polmear. 



It may here be noticed, that the mineral substances confined 

 to the granite (or rather not yet discovered in the superincum- 

 bent rocks also), are few in number. Apatite, pinite, andalusite, 

 and, I believe, uranite, at present complete the list. 



Short Hock. — This binary compound, too generally known to 

 need any description here, is usually found on the confines of the 

 granite in such large masses as to render us doubtful what name 

 to assign to them. Indeed our geological guides have not as 

 yet furnished us with a very definite or accurate terminology for 

 the purpose. What one observer would describe as a large dyke 

 or patch, another would, perhaps, elevate to the dignity of a 

 formation. Roche has been constantly noticed as presenting a 

 magnificent display of this rock ; and Mr. Sedgwick mentions 

 it as occurring in veins traversing the granite between Lemorna 

 Cove and the Land's End (p. 19). I have observed it on the 

 large scale forming the whole of the tor named Cam Mewan, 



" Therefore, if there is any parallelism in the stratification of the killas, the granite 

 must be considered not as an alternation but a vein. At Dolcoath, the floor of granite 

 is said to be nearly horizontal ; most of the killas in the neighbourhood is, if I do not 

 err, considerably inclined. (See Thomas's Report, p. 34.) 



t Mr. Sedgwick appears to have determined this point as far as our present means of 

 examination permit. (P. 34.) 



$ We obtained some highly illustrative at Costellow's Mine, near Roche. 



