ASSOCIATED ROCKS OF THE LIZARD DISTRICT. 887 



At the south-west corner of the Lizard peninsula is a mass of 

 talco- micaceous shales, described by De la Beche (p. 29), and sepa- 

 rated in his map. As far, however, as I can make out, they only 

 form a zone with some slight lithological peculiarities in the horn- 

 blendic schist, into which they seem to pass almost insensibly. These 

 may be well studied in the descent to the shore at Polpeor, and in 

 the base of the cliffs there. 



The Western Coast. 



Following the cliffs from Polpeor for about a mile in a straight 

 line, we come to the first junction with the serpentine, at the south 

 end of the narrow strip of sand called Pentreath Beach ; a little 

 chine runs almost along the line of junction. To make out the 

 relations of the two rocks here is no easy task ; both are extremely 

 decomposed for some yards, and traversed hy numerous cracks, which 

 are filled with calcite, often stained red with haematite, and project 

 like a network from the weathered ground. The rocks are thus 

 almost brecciated in situ. The difficulty is caused by the close 

 resemblance of the two rocks in their extremest decomposition, so 

 that it is sometimes almost impossible to separate them. After two 

 or three visits and a most minute examination, I think I have suc- 

 ceeded. The cliff on the north bank of the little chine is all ser- 

 pentine ; on the south the headland is all hornblende schist ; but 

 after a few yards the serpentine rises from the shore and forms the 

 lower part of the cliff, its boundary curving gradually upwards. 

 Thus there is not really a passage from the one rock to the other 

 here, or a faulted junction, but the serpentine is intrusive. The 

 serpentine then forms the cliffs as far as they can be followed ; above 

 them, near the upper end of the beach, and some 50 feet above it, a 

 granite vein breaks in two or three places through the serpentine, 

 which is cracked and altered at the junction ; the granite is finely 

 crystalline, chiefly composed of quartz and felspar, with only a 

 little mica ; it is of a pinkish grey colour, becoming red and friable in 

 weathering. One mass has carried up some irregular fragments of 

 hornblendic schist. Close by is another mass of hornblendic schist, 

 included in the serpentine, possibly forced into it by the granite ; 

 and another included mass may be seen on the beach below. On the 

 hillside, a short distance beyond, is a serpentine-quarry. Two of 

 the varieties of the rock obtained here are very pretty (no. 1 *) :— one, 

 of a dull red colour, irregularly mottled with a waxy-looking dull 

 green mineral, with occasional flakes of greenish bronzitef, rather 

 hard and irregular in fracture ; the other, a dull purplish red, veined 

 with greyish green, the latter generally fringing a thin dark line, 

 like a crack, and forming a sort of polyhedral network. It is pro- 

 bably only the result of decomposition, but produces a very pretty 

 effect. At the north-east angle is a bifurcating granite vein, about 



* These numbers are for reference in the microscopic descriptions, 

 t Until I come to the microscopic examination of the serpentine, I shall use 

 this term as generic, to include either metalloidal diallage or enstatite. 



3m 2 



