ON Tin; c'u\::st\llim; kocks of tiii; i,i/aiu) distiuct. 48."> 



district. The most streaky serpentine on the eastern coast, south of 

 the Manacles, is the dark variety on either side of Caerleon Cove, 

 but here the gabbro is not markedly foliated. The serpentine at 

 Pen Voose, except for slii^ht and very loctd crushing near faults, is 

 perfectly normal. 80 it is in the neighbourhood of the great 

 Carrick-Luz dyke, where the foliation in the gabbro is at a maximum. 

 About Enys Head streaky serpentine and gabbro, sometimes foliated, 

 occur together, but there does not appear to be any necessary con- 

 nexion between the structures. 



(3) The gabbro and serpentine are sometimes welded together, 

 sometimes separated ; the former condition is perhaps more common 

 in Coverack Cove than elsewhere, and is more usual with the thin 

 veins than the larger masses. 



(4) The gabbro is often rather variable in texture. The great 

 mass of Crousa Down appears to be the most uniform in this respect, 

 and it consists of medium-sized grains, though occasionally small 

 patches of coarser varieties occur along the coast. The Carrick-Luz 

 mass is more coarsely crystalline. All the smaller dykes, as a rule, 

 are coarse-grained, and even in the thinnest veins the rock generally 

 does not become fine-grained, but maintains a medium texture. 

 Some of the largest crystals of diallage occur in masses less than, a 

 foot thick. Even in the same mass the gabbro not seldom exhibits 

 considerable variation in texture, the ordinary coarse kind being 

 streaked or mottled with vaguely -defined patches of finer grain. 



Fig. 4. — Gdbhro veins near a ' natural arch ' on the shore, 

 west of the Carrick-Luz mass. 



. » • • tj'in • » • 9 • • • A*y* *■ * 

 « • • • * • -A Vl- •• •"•••//«/* 



1. Serpentine. 



2. Coarse gabbro. 



3. Moderately foliated gabbro. 



4. Very foliated gabbro. 



(5) The foliation sets in and disappears in a most capricious fashion. 

 Part of a dyke, an arm of a vein, may be foliated (fig. 4), without 

 any apparent reason or connexion with any structure in the adjacent 

 rock (especially when this is serpentine), and the rest may be normal. 

 The significance of the relations of the ordinary and the foliated 



