312 SERPENTINE OF CORNWALL. 



Serpentine. 



Serpentine of the Lizard. The serpentine district of the Lizard 

 is a wild moorland plateau furrowed by gullies and small coves with 

 cliffs, which often rise vertically for from one to two hundred 

 feet. 



In this area, besides serpentine, the rocks shown are gabbro and 

 hornblende schist, with some granite and dolerite. The first junc- 

 tion of the serpentine on the west coast is seen near Polpoer. On 

 the north of a little chine the brecciated rock is all serpentine, on the 

 south it is hornblende schist. The serpentine is intrusive ; near by 

 other masses of hornblende schist are included in the serpentine, which 

 is sometimes dull-red, mottled with a dull-green mineral and occa- 

 sional flakes of bronzite. The different varieties which it exhibits 

 are all the result of decomposition. The rock is cut through by 

 veins of granite in many places, and at the contact the serpentine is 

 altered. At Cadgwith the rock is black ; it contains, according to 

 Mr. Hudleston, 36 per cent, of magnesia, 38 per cent, of silica, 12 

 per cent, of water, 8 per cent, of iron, and 2 per cent, of lime in the 

 matrix freed from crystals. 



On the east coast the exposures are even more complicated than 

 on the west, the hornblende schist being frequently included in the 

 serpentine, while the latter rock is cut by gabbro veins and by 

 granite. The gabbro is of two ages ; the older variety has a dull-red 

 ground mass, with greyish-white felspar and small crystals of diallage, 

 and may easily be mistaken for serpentine. The newer gabbro is 

 coarser in texture and more decomposed. Professor Bonney believes 

 the intrusion of the serpentine took place after the metamorphism of 

 the hornblende schist, and that the metamorphism of the serpentine 

 was complete before the intrusion of the gabbros and hornblendic 

 dolerites which are found on the east coast. 1 



The Lizard serpentine contains olivine, enstatite, olive green with 

 a metallic lustre, diallage, hornblende, augite, chrysolite, picotite, be- 

 sides magnetite, occasionally a little felspar, and products of decom- 

 position, such as steatite. It closely resembles Iherzolite, and is 

 regarded as an altered peridotite intrusive in hornblende schist. 2 



Among the localities described are Coverack Cove, Mullion Cove, 

 Gue Graze, Lower Pradanack Quarry, Hill Quarry, Helston Road, 

 Goomhilly Downs, Kynance Cove, George Cove, Cam Sparnack, 

 near Cadgwith, and Balk. 



Serpentine of Anglesea. Serpentine occurs at several localities 

 in Anglesea and in Holyhead. It is found in a bluish or greenish 

 schist, which is greatly crumpled near Ty Newydd, and is itself cut 

 through by gabbro, which sometimes has a serpentinous aspect. 

 Sometimes the serpentine is reddish, brecciated, and veined with 

 calcite. A larger mass of serpentine occurs near Rhoseolyn, at the 



1 Bonney : Q. J. G. S., vol. xxxiii. p. 884. 



2 Q. J. G. S., voL xxxix. p. i. 



