146 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 16, 



bands above noticed, which run along the Carnarvon chain, from 

 Carnedd Llewelyn through Cwm Idwal, and thence by the top of 

 Snowdon and the top of Moel Hebog. 



There are probably great dislocations along the valley extending 

 from Dolgelly to Bala, especially as, near the line of section, there 

 is a considerable change of strike ; for the masses ranging up to 

 Arrenig, Arran Mowddwy, &c. strike nearly N.N.E., while those to 

 the south of the sectional line strike through the chain of Cader 

 Idris, about N.W. and S.E. Be this as it may, all the bedded masses 

 (with the exception of certain disturbed beds near the valleys) dip 

 in succession towards the S.E. 



Continuing the section to the south-east side of the valley, we 

 again cross a mountain ridge (connected with Arran Mowddwy), in 

 which we have regular beds of slate with two or three enormous 

 ribs of igneous and other associated rocks. These are followed in 

 the same ascending order by a great series of rocks, through which 

 passes the Bala limestone ; and the whole is overlaid (agreeably to 

 the statements of my former papers*) by great disturbed beds of 

 unconformable Upper Silurian rocks. 



I do not profess to describe the upper beds of the preceding 

 section. They terminate in a series of rocks nearly on the same 

 parallel with those exhibited in a section drawn from the great 

 Merioneth anticlinal over the top of Great Arrenig, and thence to 

 the top of the Berwyn chain. Indeed these two sections are through 

 the same part of the great Cambrian series. The Arrenig section is 

 however more instructive in some of its details, and contains (at the 

 least) three bands of limestone with numerous fossils, as has been 

 shown in former papers ; but it terminates abruptly, and is not over- 

 laid by any Upper Silurian groups. 



Section VI. 



From the great Merioneth Anticlinal through the Chain of 

 Cader Idris. 



From Barmouth to the Valley of the Dyfi. 

 TwrMawr. Valley below 



Tal-y-Uyn. E.S.E. 



I suppress, as far as possible, all unnecessary details. All I attempt 

 is, to put the chain of Cader Idris in coordination with the other older 

 deposits of North Wales, and to show that it is included in the same 

 general system of undulations. The group of mineralized slates 

 which (in describing the preceding section) I provisionally identified 

 with the Festiniog flags (Lingula beds), passes along the course of 

 the Maw to the point where it enters the plain below Dolgelly. 

 Taking the strike of these beds, from a point near Llanelltyd, as 

 guide for a compass-bearing, I found that the same beds might be 

 looked for on the south side of the Barmouth estuary near Ty Gwyn. 



* See Journal, vol. i. p. 10. 



