302 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



but as you advance towards the north, the igneous rocks become 

 more and more prevalent. 



To the north and west of Conway there is an extensive district of 

 metamorphic rocks, of which the most abundant is quartz-rock, in 

 various forms, but usually more or less schistose. 



South-west part of Carnarvonshire, 



1. Schistose Rochs. — The strike of the beds, which, in the Car- 

 narvonshire trough, is from N.E. to N.N.E., changes to east a few 

 miles south of B.eddgelert, and a little further to the south becomes 

 perpendicular to" the strike prevailing in the trough. 



At Forth Treweddyn, ^\ miles south of Beddgelert, in extensive 

 quarries of light grey flagstone, the bedding dips north 20°, the 

 cleavage N.N.E. 30°. About a mile west of Forth Treweddyn, in 

 the high crags north of Tremadoc, a remarkable instance occurs of 

 the interstratifi cation of greenstone with the schist. 



The schist on which the village of Tremadoc stands is very much 

 altered and broken. It dips N.N.E. 15°, and passes beneath a thick 

 mass of greenstone, running two miles westward. The same dip 

 prevails in several hillocks south-east of Tremadoc, between that 

 village and Forth-madoc; the rocks consisting of a ferruginous 

 grit alternating with beds, four inches thick, of very rich ironstone. 

 Immediately to the south-west of Forth-madoc, near Morfa Lodge, 

 is a light grey flagstone, dipping N.N.E. 10°. 



West of Morfa Lodge is the greenstone ridge of Moel-y-gest, 

 which has raised the schists into an anticlinal ridge, and given them 

 an eastern strike. On the line of the axis of this ridge, three miles 

 west of Morfa Lodge, the beds have a north-east strike ; and in 

 a metamorphic rock, which dips south-west 30°, a copper-mine is 

 worked. 



From Brongader to the south-west as far as Criccieth, a distance 

 of about two miles, schistose rocks extend. They dip south. To 

 the south of Criccieth the schistose beds are much concealed by 

 great accumulations of gravel. 



About seven miles west of Criccieth, and four miles north of 

 Fwllheli, is a quarry beside the road from Fwllheli to Carnarvon, 

 in which the beds strike north and south. Here, in a dark slate of 

 indifferent quality, are found obscure traces of organic remains. 

 The bedding dips west .^5°, the cleavage west 70°. 



The rest of the south-west part of the county, frequently called 

 the heel of Carnarvonshire, is covered by a brown, very rotten and 

 shivery schist, in which the author did not discover any organic 

 remains. The schists are broken up by various porphyritic masses, 

 and their strike and dip are very irregular. 



In the proximity of the felspathic rocks, hereafter noticed, these 

 schists are changed into black shale ; the resemblance of which to 

 a coal-shale has, in several places, given rise to borings for coal. 

 One of these trials was made between Criccieth and Fwllheli ; and, 

 on a common about 2J miles west of the latter place, the borings 



