304' PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



At Porth-felin, on the south, a narrow ridge of mottled green 

 and red serpentine, associated with green trap, blood-red jasper, 

 and a crystalline flesh-coloured limestone, breaks through between 

 two nearly vertical ridges of greenish-white steatitic schist. The 

 ridge runs N.N.E. and S.S.W, The cleavage of the schist, in the 

 western ridge, dips south-east 50°. At Forth Orion, three miles to 

 the N.N.E., a limestone, similar to that last mentioned, is said to be 

 found. 



At Porthwen and at Edeyrn, near Nevin, the serpentine runs be- 

 tween the greenstone, as if ejected at a more recent period. At the 

 northern extremity of the serpentine band, the serpentine is pure, 

 and of a dark green colour. 



Merionethshire. 



Barmouth chain of Hills. — Barmouth lies at the southern point 

 of a lofty chain, which after running northwards nearly fourteen 

 miles, is cut off by the great Bryn-y-ddinas fault. This chain is 

 chiefly remarkable for the interstratification it exhibits of schistose 

 with igneous rocks. 



The axis of the lofty hill immediately north of Barmouth is a 

 mass of compact, highly crystalline, lightish-coloured greenstone. 

 On the west side of the hill are numerous alternations of schist and 

 greenstone. At first the greenstone predominates, and the schis- 

 tose beds are thin and far apart ; but as the distance from the axis 

 increases, they become more frequent, until, at a mile from it, the 

 greenstone wholly disappears. 



The schistose beds are of variable thickness ; those of greenstone 

 are, many of them, only a few inches thick, and some many feet. 

 The cleavage planes can, in many cases, be traced through the 

 greenstones, but they do not lie close together, and are only faintly 

 marked. 



On the east side of the end of the ridge, near Barmouth, the 

 alternations of greenstone are fewer than on the west side. About 

 a quarter of a mile east of Barmouth the greenstone ceases, and the 

 chain is overlaid by a great thickness of hard light blue slaty flag- 

 stone, and above this are grey schists. 



Towards the southern end of the chain the prevailing strike is 

 north by east. Near Barmouth, on the west side of the chain, the 

 bedding dips south-east 30°, and the cleavage north-west 60°. 

 About a mile north of Barmouth, on the Harlech road, the bedding 

 dips E.N.E. 60°, and the cleavage E.S.E. 80°. East of Hendre- 

 mynech, which is about a mile north of the town, the cleavage is 

 vertical, and strikes N.N.E. East of Barmouth the bedding dips 

 E.S.E. in a steep arch ; the cleavage is vertical, and strikes N.N.E. 



Towards the north end of the chain the alternations of igneous 

 with aqueous rocks are on a greater scale. The sides of Cwm- 

 moch, leading from the north-west up to Diphwys, aff'ord a good 

 section of these beds. Greenstone, similar to that of Barmouth, in 

 beds from three to ten feet thick, alternates witii thinner beds of 

 sandstone and conglomerate, which are often semi-crystalline, and 



