SHARPE ON NORTH WALES. 303 



were continued until the tools were broken by coming in contact 

 with porphyry. 



At the extreme point of the south-west promontory of Carnar- 

 vonshire, between Aberdaron and Porth-felin* hard gritty schistose 

 flags are found ; and these are overlaid by rotten brown schists, 

 striking north-east or N.N.E., and dipping at a very high angle to 

 the south-east ; the cleavage here dips south-east 50°. 



The schistose rocks of the south-west of Carnarvonshire (with 

 the exception of the steatitic schist hereafter noticed) are referred 

 by the author, though with much hesitation, to the Cambrian series 

 of rocks. 



Note, 1846. — From organic remains found in them by Professor Sedgwick, it 

 is now known that they belong to the Lower Silurian series, and they are accord- 

 ingly coloured as such on the annexed map (see Plate XII.). 



2. Igneous Rocks. 



(a.) Felspathie Porphyry. — The insulated hili south of Criccieth, 

 a considerable tract round Pwllheli, and the hills which commence 

 on the coast 3| miles south-west of the latter place, and run north- 

 west from Mynydd-tir-y-Cwmmwd, south of Llanbedrog, through 

 Mynydd-mynytho to Carn Fadryn, consist of an amorphous flesh- 

 coloured rock, composed of compact felspar and quartz, and resem- 

 bling the rocks of Cader Idris and Arenig. In the ravine of Nant 

 Bodlas, which intersects the last-mentioned felspathic mass, between 

 Mynydd-mynytho and Carn Fadryn, black, grey and flesh-coloured 

 porphyries occur. Felspathic rocks are also found on a line com- 

 mencing in Mynydd Ystvvm north of Aberdaron, and extending, in 

 a north-easterly direction, through Mynydd- cefn-aralwch to the high 

 peaks of Yr Eifls and the hill south of Clynnog-fawr. 



These felspathic rocks, when in proximity with the schist, disturb 

 its planes both of bedding and cleavage, and alter its mineral cha- 

 racter. 



(6.) Greenstone, — The greenstones of the south-west of Carnar- 

 vonshire, not including those of Tremadoc, differ from those of the 

 Snowdon chain in two respects. First, they are of coarser grain ; 

 and secondly, they are of posterior date to the cleavage of the 

 schists. Like the felspathic rocks last noticed, they have been up- 

 heaved in great masses, causing much confusion in the schistose 

 rocks. Of this description of greenstone consist the hills of My- 

 nydd Ilhiw, four miles east of Aberdaron, and of Carn Boduan 

 south of Nevin ; also the low rocks of Edeyrn west of Carn Boduan, 

 and of Porthwen on the coast further westward ; and to the north- 

 east, the hills of Moel Penllechog and Y-gyrn-ddu, south-west of 

 Clynnog-fawr. To the north of Y-gyrn-ddu, at the points of junc- 

 tion between this greenstone and the porphyry of Y-gyrn-coch, 

 several varieties of igneous rock occur. 



(c.) Serpentine and Steatitic Schist. — Along the western coast of 

 the Carnarvonshire ])romontory, from the ]K)int opposite Bardsey 

 island to Porth Dynllaen, west of Nevin, a band of serpentine and 

 steatitic schists extends. 



VOL* II. — PART I. X 



