A HISTORY OF CORNWALL 



pentine. A large mass of gabbro forms the cliffs between Coverack 

 and Manacle Point, and extends inland for about 4 miles as an ovate 

 mass occupying an area of 6 or 7 square miles, including the districts 

 of St. Keverne and Crousa Downs. A smaller mass mile in width 

 extends inland from the headland of Karakclews to Gwinter. Another 

 considerable exposure occurs on the shore near Landewednack. 



According to Mr. Teall the principal constituents of the Lizard 

 gabbro are plagioclase, augite or diallage, hornblende, olivine and 

 saussurite, while original iron ores are rare or altogether absent. 



The dioritic rocks that occur in this region appear as veins in the 

 gabbro, and as part of a banded series consisting mainly of diorite and a 

 fine grained granite. In places the two latter types vein each other, 

 while they sometimes occur together as parallel bands. Mr. Teall 

 describes the constituents of the dioritic rocks as felspar, biotite, green 

 hornblende, sphene, iron ores and apatite. 



The granite of the Lizard peninsula occurs as veins in the serpen- 

 tine, gabbro and dioritic rocks, and is of different character from the 

 Cornish granite already described from beyond that region. That of the 

 Lizard has been deformed into schist. It veins the serpentine at 

 Kynance, a dioritic rock at Pen Voose, and occurs in a gabbro north of 

 the last-named locality, and also veins a diorite at Kennack Cove. 



Hornblende schist forms a wide band at the northern edge of the 

 Lizard complex and appears to extend practically right across the pen- 

 insula from sea to sea. This rock differs from the hornblendic rocks 

 described from beyond the Lizard area in the frequent development of a 

 highly banded character, which is so perfect that viewed from a short 

 distance the white and green striping, representing the differentiation of 

 the felspathic and hornblendic minerals, strikes the eye as a parallel 

 arrangement of almost mathematical precision. 



Between Porthoustock and Landewednack greenstone dykes occur 

 in the gabbro and serpentine, ranging from epidiorite to hornblende 

 schist, while in some a certain amount of pyroxene still remains. 

 But in the neighbourhood of Coverack there are found dykes of olivine 

 dolerite which have retained their original character. 



In the southern portion of the peninsula there is a zone of fine 

 micaceous and actinolitic schists which in the outlying islands have 

 reached a still further stage of metamorphism, and as pointed out 

 by Mr. Howard Fox consist of typical gneiss. As remarked by Mr. 

 Teall this zone of intense mechanical metamorphism includes lenticles 

 and bosses of greenstone associated with actinolitic and hornblende schists, 

 the latter having originated in part at least from the metamorphism of 

 the former. 



In recent years keen controversies have arisen among geologists 

 regarding the origin of the foliated igneous rocks and the relative ages of 

 the serpentine and hornblende schists. On one hand it is contended that 

 the foliation of the gabbro and the passage of dykes of porphyritic epidio- 

 rite into hornblende schist have been produced by dynamic metamor- 



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