Vol. 59.] GKANITE AND GREISEN OF CLIGGA HEAD. 143 



and a little cassiterite are mentioned as occurring in the greisen ; 

 cassiterite, wolfram, lithomarge, lepidolite, and mispickel as being 

 found in the quartz-veins traversing the centres of these greisen- 

 bands. Concerning this description of Cligga Head, we can only 

 wish that Prof. Le Neve Foster had had more time to devote to 

 what he very justly described as one of the most magnificent 

 sections in Cornwall; for, although brief, his paper contains a 

 very graphic account of the principal characteristics of the section 

 of the granite which faces westward. 



During the summer of 1902 I was engaged in re-mapping the 

 country round Perranporth and St. Agnes, and found that there was 

 still much to be said concerning the Cligga-Head granite, which 

 affords an ideal opportunity of studying metasomatic alteration in a 

 tin-bearing district. Although formerly easy of access, the Cligga 

 section is now on the grounds of Nobel's Explosive Factory, es- 

 tablished on the promontory a few years ago. But, thanks to the 

 courtesy of the manager, Mr. Joseph Turner, I was enabled 

 to make several visits to the headland ; and I am anxious here to 

 record my indebtedness both to him and to his son, Capt. Turner, 

 for their unfailing efforts on my behalf, in giving me every assist- 

 ance in their power. To Capt. Turner I owe an especial debt of 

 gratitude for his help, which considerably lightened my task, in 

 examining the granite-section. 



It is necessary first to give a brief sketch of the geology of this 

 part of Cornwall. The ' country ' is kill as, composed chiefly of 

 bands of felspathic mudstones with grey shale-partings, striking 

 roughly east and west, and disturbed by innumerable dislocations. 

 Two elvan-courses, which can be traced for some miles, cut this 

 strike obliquely, trending 20° north of east : one the St. Agnes elvan, 

 a typical quartz-porphyry ; the other, the granitic elvan of Perran- 

 porth. Nearer the Cligga granite are several outcrops of smaller 

 elvans similar to the St. Agnes elvan. The nearest large mass of 

 granite is that of Eedruth and St. Day, 9 miles distant ; while the 

 St. Austell mass is 14 miles away to the east. There is, however, a 

 small granite-outcrop much nearer, that of St. Agnes, only 4 miles 

 distant : this patch of granite, although very badly exposed, pre- 

 sents interesting points of similarity to the Cligga mass, as will be 

 shown later. That the Cligga-Head granite was intruded into the 

 killas like the other, and larger, granite-masses of Cornwall, there 

 can be no question ; for the metamorphism, which results in a brown 

 ■tourmaline-rock at the junction, 1 and in bleaching and spotting of the 

 shales and mudstones for some distance beyond, is strongly marked. 

 Although this spotting is generally a most unsatisfactory guide 

 when attempting to map an aureole of metamorphism in Cornwall, 

 it was found possible in this case to draw a satisfactory boundary ; 



1 Prof. Le Neve Foster, in Trans. Koy. Geol. Soc. Cornw. vol. ix (1878) 

 p. 218, records molybdenite from the altered killas at the junction, but no one 

 has been fortunate enough to find it again. 



