142 ME. J. B. SCRITENOK ON THE [May I903, 



14. The Granite and Greisen of Cligga Head (Western Corn- 

 wall). By John Brooke Scrivenor, Esq., M. A., F.G.S. 1 (Read 

 February 4th, 1903.) 



[Map on p. 144.] 



The small mass of granite known as Cligga Head, forming a bold 

 promontory between St. Agnes and Perranporth on the northern 

 coast of Western Cornwall, has long been known, not only to the 

 geologists of that county, but also to others from farther afield. 



Conybeare, 2 in 1817, from notes by Buckland, described a small 

 formation at Cligga Point which would 'probably be considered 

 by the Wernerian school as the newer granite,' and remarked on tho 

 stratification and the fact that it was worked for tin. A sketch also 

 is given of the headland {op. cit. pi. xxiii), which does not, however, 

 show the leading features exactly as they occur. 



In 1818, Joseph Carne 3 spoke of granite at Cligga Head, appa- 

 rently stratified obliquely, but proving, on a nearer view, to be 

 traversed by small veins of ' blackish quartz, whose contem- 

 poraneous formation can scarcely be doubted.' In a footnote the 

 same author wrote : — 



' The granite at Cligga Point (if it is not a large elvan-course) might be called 

 secondary or transition granite, without affecting the age of the granite of other 

 parts of Cornwall, as it is far from the large granite-chain ' {op. cit. pp. 74-75). 



In 1820 Sedgwick 4 gave a description of the granite, as resembling 

 the common granite of the country, except the ' intermediate parts,' 

 which exhibited varied modes of aggregation : the strong folding of 

 the parallel k beds' in the granite was also noticed. 



(Eynhausen & Dechen/ in 1829, noted the ' numberless veins 

 of granite which intersect the granite itself,' giving a stratified 

 appearance to the rock. 



Boase in 1830, and Henwood in 1838 7 and 1843, 8 gave accounts 

 of the mineral composition of the mass, the latter author empha- 

 sizing the 'jointed ' structure and variation in composition. 



Prof. C. Le Neve Foster 9 was, it is believed, the first to explain 

 the true nature of the phenomena seen at Cligga Head. In 1877 

 he described and illustrated the alternation of granite and greisen, 

 which produces the stratified appearance, attributed this formation 

 of the greisen to vapours acting on the walls of fissures, and showed 

 that the mass found a parallel, not only in the mode of occurrence of 

 the greisen, but also in the curvature of the veins, in the tin-lodes 

 of Zinnwald. Besides quartz and muscovite, tourmaline, gilbertite, 



1 Communicated by permission of the Director of H.M. Geological Survey. 



2 Trans. Geol. Soe. vol. iv (1817) p. 401 & pi. xxiii. 



3 Trans. Boy. Geol. Soc. Cornw. vol. ii (1822) p. 80. 



4 Cambr. Phil. Soc. Trans, vol. i (1822) p. 131. 



5 Phil. Mag. & Ann. vol. v (1829) p. 169. 

 c Trans. Eoy. Geol. Soc. Cornw. vol. iv (1832) p. 303. 



Twentieth Ann. Eep. Eoy. Inst. Cornw. (1838) p. 29. 

 Trans. Eoy. Geol. Soc. Cornw. vol. v (1843) p. 93. 

 Ibid. vol. ix (1878) p. 213. 



