1.3(3 J. A. PHILLIPS OX THE SO-CALLED 



of their characters, and their distinct nature, however, I am sure 

 that, whether rightly named or not, they are as well entitled to 

 appropriate appellations as any rocks can be. 



" By felspar rock I mean a rock of small granular structure, con- 

 sisting, apparently, principally or almost wholly of felspar. By 

 slaty felspar I mean a rock apparently of the same composition, or 

 only with the addition of a very small portion of mica, with a dis- 

 tinct slaty fracture. 



" These five rocks, constituting the assemblage to which I have 

 given the name of the slate formation, occur in beds of various 

 magnitude, alternating with each other ; but, with one very small 

 exception, I have uniformly found the slaty felspar rock in imme- 

 diate contact with the granite ; and I think it not improbable that, 

 in proportion as we recede from this central rock, we shall find the 

 slaty felspar become less frequent, and be finally superseded by 

 some of the varieties of clay-slate"*. 



Dr. Forbes subsequently goes on to say that, in tracing the shore- 

 line from Mousehole to Newlyn, nineteen different beds may be 

 distinguished ; and he remarks that, in advancing from Newly n to 

 Penzance, the rocks consist of a series of hornblendic beds of a more 

 or less slaty character, together with slaty rocks intermediate be- 

 tween felsite and hornblende slate. He describes the rocks imme- 

 diately south of Penzance pier as being precisely similar to the 

 others, excepting that the hornblendic varieties have more decidedly 

 the character of greenstone, and that the slaty rocks approximate 

 more closely to clay-slates. Of this locality he further remarks, that 

 several of the beds are decided and well-characterized clay-slates. 



The rocks extending from the pier to Chyandour are stated to be 

 similar to those between Xewlyn and Penzance ; but their dip, 

 direction, and succession are described as being somewhat less dis- 

 tinct. The same author calls attention to a greater irregularity in 

 the direction and inclination of the strata between Marazion and 

 Cuddan Point. 



With the view of ascertaining the correct names of some of the prin- 

 cipal Cornish rocks, Mr. John Hawkins forwarded, in 1793, a care- 

 fully selected collection of specimens to Prof. Werner, and during the 

 autumn of the same year received the decision of that then eminent 

 petrologist. Mr. Hawkins tells us, "no doubt was expressed of the 

 nature of our metalliferous rock, the ~killas." It was pronounced to 

 be a genuine Thonschiefer, or argillaceous slate, in no respect differ- 

 ing from that which occurs in Saxony Those taken from the 



neighbourhood of Penzance were, after a rigid scrutiny, pronounced 

 to be hornblende-rock, intimately mixed with the constituent mass 

 of argillaceous slate, and in part genuine hornblende-slate" f. 



Writing in 1827, Messrs. Von Oeynhausen and Yon Dechen 

 remark, " the Killas (of Cornwall) is, at its contact with the 



* " On the Geology of the Land's End District," by John Forbes, M.D. 

 (Trans. Royal Geol. Society of Cornwall, vol. ii. (1822) p. 251). 



t 'On the Nomenclature of the Cornish Rocks,' by John Hawkins, Esq.. 

 F.R.S. (Trans. Royal Geol. Society of Cornwall, vol. ii. (1822) p. 155). 



