230 GRANITE MASSES IN DEVON AND CORNWALL. 



besides smaller patches at St. Michael's Mount, Tregonning and Godol- 

 phin Hills, Cam Brea, Cam Marlts, near Redruth ; Cligga Point, 

 near St. Agnes ; Castle au Dinas and Belovely Beacon, near St. Columb 

 Major and Roche ; Kit Hill and Hingston Down, near Callington ; 

 and at Lundy Island. 1 



The range of the granite is 24 JST.E. Schorl is chiefly developed 

 in it on the confines of the various masses. 



Dartmoor. The granite of Dartmoor is coarse-grained, with the 

 mica sometimes white, sometimes black. It is schorlaceous where it 

 joins the slates. The schorl often occurs in radiating nests, especially 

 to the west of Buckfastleigh, but ordinary granite often passes into 

 schorl rock. After the mica disappears, the felspar vanishes, and 

 the rock at last consists of quartz and schorl. Schorl rock is seen at 

 Holne Lee. 



Bodmin Moor. The granite of the Brown Willy district is similar, 

 consists of quartz, felspar, and two micas, is often porphyritic, but 

 not particularly schorlaceous, though schorl enters into its composition 

 near St. Cleer. 



St. Austell. The granite district of St. Austell or Hensborough 

 is much more variable, and much richer in schorl than those of either 

 Brown Willy or Dartmoor, and is more decomposed. On the west of 

 this district the mica becomes scarce and often absent, and is replaced 

 by a talcose mineral and schorl. Schorlaceous veins are abundant in 

 the St. Austell granite in the western and central portions. A thick 

 vein of dark mica traverses the granite of St. Dennis Down. 



Cam Menelez. The Cam Menelez or Falmouth granite is occa- 

 sionally porphyritic from the presence of felspar crystals, but the 

 grain is regular at Constantine and Mabe. It is poor in schorl. 



Land's End. At the Land's End the granite abounds in schorl, 

 and often passes into schorl rock, as on the west of Penzance, at 

 Leity, near Lelant, and on the east of Trecobben Hill. At Trevalgon, 

 near St. Ives, the schorl rock contains large crystals of felspar. The 

 schorl veins in the granite at Wicca Cove, near Zennor, -are often 

 several inches thick. This granite contains much pinite. 



Scilly Isles. The granite of the Scilly Islands is a somewhat 

 coarse compound of quartz, felspar, and the two micas. Schorl is 

 rare. It is traversed by veins in which the grain is finer. 



De la Beche remarks that schorlaceous veins occur in the granite 

 of Kit Hill, and that the mass of Belovely Beacon graduates into 

 schorl rock on the north. The granite of St. Agnes Beacon is on the 

 north a mottled mass of quartz and felspar, containing large crystals 

 of flesh-coloured felspar and semi- crystallised quartz ; on the south the 

 rock becomes more quartzose, and is fine-grained and traversed by 

 small veins and strings of black oxide of tin. 



On the coast it is composed of quartz, felspar, and a talcose 

 mineral, with occasional specks of mica, and is often marked by lines 

 of felspar crystals. At Godolphin Hill the rock is a base of felspar 



1 " Report on Cornwall, Devon, and West Somerset, De la Beche," 1839, p. 156. 



