of Devonshire and Cornwall. 129 



of St. Kevern, there is no more graiiwacke. Before coming to the 

 serpentine in situ^ a rock intervenes, composed of felspar and diallage 

 which I traced very distinctly as far as Treleever, a hamlet about 

 four miles S.S.E. of St. Kevern. The felspar of this rock is com- 

 pact and opaque, v^^lth a tendency to crystallization : the diallage 

 belongs to the variety called diallage mefallo'ide by Haiiy : its co- 

 lour varies from bronze green to a brilliant grey, and it presents very 

 smooth rhomboidal joints ; sometimes the felspar prevails in the 

 mass, but most frequently the diallage. This rock is extremely tough, 

 when struck it makes the hammer rebound. There is a quarry of 

 it in the village of St, Kevern, where it is blasted with gunpowder. 

 From what I have seen of the serpentine district, I believe that it is 

 confined to that portion of the country, which lies to the south of a 

 line stretching east and west, from the neighbourhood of Treleever, 

 by Ruan Major, as far as Lower Pradanack ; thus including the pro- 

 montory, the extremity of which is called the Lizard Point. It is pos- 

 sible, however, that the serpentine may extend beyond these limits, or 

 that it may be irregular, as we have found the grauwacke to be ; but 

 it is not an object of much importance whether it is so or not. I 

 must not omit to mention, that in the space which the serpentine 

 occupies, there are two formations of rocks in subordinate beds, and 

 of different natures : the one mica slate, which is met with to the 

 S.S.W. of the village of the Lizard, on the vcay to the light houses, 

 where it forms the cliffs, and appears to extend into the sea, forming 

 those dangerous reefs and sunken rocks, which are seen beyond the 

 Lizard Point : the other is the soap-rock to the north of Kinance 

 Cove. 



The serpentine of the Lizard Point is not homogeneous in its 

 composition ; the colour of the base is usually leek green, and the 



R 



