SHARPE ON NORTH WALES. 305 



with beds of schist. The dip is from N.N.E. to N.N.W., at an angle 

 of 15°. 



On the west side of Craig-drwg (a ridge commencing about 

 eleven miles north of Barmouth, and IJ mile long), on the descent 

 towards Harlech, in a similar series of alternations there are nearly 

 100 beds of greenstone. The bedding dips from south-west to 

 W.S.W. 10°, and the cleavage north-east 60°. 



Between these igneous rocks and the sea is a series of light blue 

 slaty flagstones, with some alternations of shale, and a few thick 

 interstratified masses of greenstone. The lowest beds of the series 

 occur near Harlech. 



On the hills behind Llanbedr (seven miles north of Barmouth), 

 and in the ravine of Egryn (three miles north of Barmouth), a bed 

 of slate is worked. The bedding of the flagstone and slate dips 

 east, E.S.E., and north-east by north, on the average east, at an 

 angle of 10°; the cleavage dips east 60°. 



Since the beds of the Barmouth chain have not been found to 

 contain any fossils, and since they are cut off by the fault of Bryn- 

 y-ddinas from the beds of the Carnarvonshire trough, the author 

 finds it difficult to determine their age with any precision. In mi- 

 neral character they much resemble the light grey slaty flagstones 

 of Manod-mawr and Ffestiniog, which are placed by the author near 

 the top of the Cambrian series. 



From the Greenstone chain of Barmouth to the Porphyritic chain 

 of Cader Idris and Arenig. — The prevailing dip on the east side of 

 the Barmouth chain near Barmouth led the author to seek for an 

 ascending series of beds in the direction of Dolgelly. The lower 

 beds are hard light grey slaty flagstones, the same probably M'ith 

 those of Harlech ; and above these are rusty schists with some beds 

 of tolerable slate. The usual dip of the beds is east at a high angle, 

 but it is subject to great irregularity, and to some alternations to 

 the south-west. The cleavage usually dips from east to south-east, 

 at from 50° to 55° ; but the angle also is inconstant. All these 

 rocks the author is inclined to refer to the Cambrian series. 



The beds in this line of section are much interrupted by exten- 

 sive igneous dikes. Near the river Mawdach these dikes strike 

 from E.N.E. to N.N.E. ; but further northward they strike due 

 north. 



The great eruptive mass of Cader Idris, which crosses the Maw- 

 dach at Dolgelly, entirely cuts ofl'the last-described series of beds. 

 Between this porphyritic chain and the parallel and similar chain of 

 Arenig, is a narrow tract of slate and schist, which crosses the road 

 to Bala, about three miles from Dolgelly. Between the porphyritic 

 chains of Arenig and Arran Mowddy, tlie beds belong wholly or in 

 part to the Lower Silurian series. 



West side of Carnarvo7ishirc, 



1. Gravel. — From Clynnog to Penman-mawr, the whole western 

 side of tlie Snowdon chain is flanked by igneous rocks, forming 



x2 



