900 T. G. LONNEY ON THE SERPENTINE AND 



curiously like vein granite ; but I am convinced all is metamorphic 

 rock. The serpentine near the junction is, as usual, much decom- 

 posed ; a line of breccia either of schist or altered serpentine extends 

 from the top of the first to the second. The northern end of the 

 third piece all but joins the fourth ; and the beds in it are absolutely 

 squeezed together by the pressure which they have undergone. Then 

 we pass another small fragment, and after about a hundred yards 

 come to two or three more, all highly altered. Another, chiefly on 

 the shore itself, occurs after about fifty yards ; and they are common 

 for the next hundred yards or so. A fragment occurs just at the 

 angle where the cliff turns inland towards the serpentine-works 

 in Caerleon Cove. Following this for a short distance we come to 

 a remarkable " greenstone " dyke at the foot of the low cliff. It is 

 from 4 to 5 feet wide ; the sides for about 6 to 10 inches are very dark 

 and compact, and so platy in structure as to be almost undistinguish- 

 able from some specimens of the hornblende schists. This structure 

 is lost rather suddenly ; and the rock assumes the ordinary aspect of 

 an igneous rock, consisting of a finely crystalline mixture of white 

 felspar and dark hornblende, with porphyritic crystals of the former 

 as much as ^ inch long. 



I have had a section made of the heart of the dyke ; and my friend 

 Mr. Allport has kindly lent me two of his own cutting, one being 

 from the outside. The former shows that the rock consists of a 

 much decomposed plagioclase felspar in long narrow crystals. The 

 interstices are occupied by a pale-coloured (generally greenish) 

 hornblende of rather fibrous or filmy aspect. There is also some 

 magnetite. The aspect of this rock is so like a typical dolerite, and 

 so unlike a diorite, that I suspect the hornblende to be a secondary 

 product, as in the gabbro. The other section is totally different, 

 and closely resembles the hornblende schist above described. I ex- 

 amined the rock at the time to see whether a piece of schist had 

 been caught up ; but if it was, I failed to detect it. 



Some of the quarries belonging to the Poltesco works are up the 

 valley inland ; but these I have not been able to visit. From Caer- 

 leon Cove a steep ascent leads us up again to the main plateau. 



Hornblende schist may be seen on the shore of the next little 

 cove, and on its left bank, above the path, intrusive gabbro*, coarse, 

 but showing a rather foliated structure, may be seen on the rough 

 grassy slope. I observed three exposures ; near to the furthest there 

 appears also to be a little schist, the rock generally on each side 

 of Caerleon Cove being serpentine. 



This rock, on the beach beyond the next headland, includes many 

 large fragments of quartzose rock, some of which very closely resemble 

 granite veins. After careful examination, however, I am of opinion 

 that they are only bands in the schist. The more quartzose and 

 harder layers have been forced among the softer, so as to mimic 

 intrusion. 



Beyond this, in cliffs of a dark serpentine, is a greenstone dyke. 



* Analyzed by Mr. Hudleston, see p. 927, 



