Vol. 55.] SERPENTINE AND ASSOCIATED E0CE:S IN ANGLESEY. 299' 



Rather towards the southern end, several of these ellipsoids or rhom- 

 boids (measuring about 6 x Ig inches) are green in the midst of 

 the whitish mass. Specimens from these have been cut, and appear 

 to be serpentine. In another slice (from rock of the northern 

 side) small wisps of squeezed serpentine appear to remain in a 

 much-crumpled talc-schist. Thus these rocks corroborate the view 

 maintained by one of us,^ that the rather similar talc-schist of the 

 Gornergrat w^as formed from serpentine by crushing and the action 

 of water. 



The small plateau yields no other example of the talc-schist, 

 but at the northern and north-eastern edge we find some evidence 

 in favour of the intrusive character of the cblorite-rock. At this' 

 part a perpendicular crag consists mainly of ' green schist,' but 

 chlorite -rock (here containing octahedra of magnetite) occurs for a 

 height of from 1 to 2 feet from the ground. It disappears for a 

 few paces, and then rises to about 10 or 12 feet. Thus the plateau 

 seems to consist of ' green schist ' with a mass of intrusive rock- 

 below protruding at the north-east, and near the quarry at the- 

 south-west, while at the latter part some serpentine (with talc- 

 schist, its still further changed representative) occurs, the intrusive 

 mass (now chlorite-schist) being posterior to both gabbro or ' green 

 schist ' and serpentine.^ In the great crush, these rocks were thrust 

 over and converted into schist. 



To the east, across the road, similar ' green schist ' ^ is quarried ; 

 it also forms the boss on which Cerig is marked in the 6-inch 

 Survey map, as well as (beyond some serpentine) several large 

 bosses in the next fields. These rise from the marsh on the 

 south, and from marshy or low land on the north-east. On 

 that side, below the large boss, in the field farther from the 

 road, chlorite-rock occurs in two places, associated in one, and 

 possibly in both, with crushed actinolitic rock, while a crumbling 

 serpentine is just seen a few yards off in the grass. In the eastern 

 boss nearer the road, we find crushed serpentine, and, about 

 10 yards away in a small scarp, which is partly masked, the 

 following succession : — chlorite-schist, talc-schist, chlorite-schist,. 

 and ' green schist ' (?). 



The soft chlorite-rock has been found in other localities. One is 

 among the 'green schists,' north-west of Plas-coch beyond the 

 marsh ; a second at the head of the large inlet south of Penrhyn" 

 Fadog. This has been already described (p. 297), and might be 

 a narrow dyke, between gabbro and serpentine. A third is from 

 north-west of Yr-ynys (west of Llyn Penrhyn), apparently here 

 near the edge of serpentine. A fourth example occurs immediately 

 west of Llyn Penrhyn (south of the stream), in a boss mainly 

 composed of serpentine. A fifth from a boss to the west of this- 



1 T. G. Bonney, Geol. Mag. 1890, p. 540. 

 ^ And to diallage-rock, if it occurred. 



3 The aspect in the field was suggestive of the modification of a compact 

 gabbro or diabase, but here also no definite evidence was obtained. 



