14 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Section IV. a. 



Craig-y-glyn, three miles and a half to the west of the line of Section IV. at 



the point marked 6. 



Horizontal base 2\ miles. 



S. Harnarmon N. 



Craig y Mynydd Mynydd 



Cefnyiodfa. Glyn. Mawr. Mawr. 



A 



Tanat, a series of slates (0), not differing in their mineralogical 

 character from the slates of the higher Berwyns ; and in these, at 

 a great depth as measured from the Caradoc sandstone, are found 

 calcareous bands, full of fossils, among which are Asaphus Buchii, 

 &c. The Craig-y-GTyn limestone {vide Section IV. a.), which 

 appears to the north of Llanrhaiadr, at the distance of nearly 

 four miles to the west of the line of Section IV., the author regards 

 as belonging to these bands. 



[The Craig-y-Glyn limestone has most of the species of the Rhiwlas lime- 

 stone ; hut the abundance of Asaphus Buchii, of Orthis compressa, of a new 

 species of Orthis, and of Encrinital stems, give it a peculiar character.} 



4. Still lower in the series are similar slates ; but they are 

 without fossils, and, after several breaks or undulations, the beds, 

 about two miles further to the north, are found to have acquired a 

 steady northern dip. 



5. South of Pont Meibion, on the Ceiriog, fossils again appear, 

 conforming to the types of the lower portion of the protozoic 

 group. 



[The lower part of the series near Pont Meibion may be only a repetition of 

 the Craig-y-Glyn series, with a reversed dip. But the higher part of the series, 

 which ranges over the crest of the Berwyns by Bwlch Llandrillo, contains only 

 Bellerophons, particularly a new species, B. nodosus, found also at Soadley, in 

 Shropshire, by Mr. Salter. At Bwlch Llandrillo, a new Orthis, O. cambriensis, 

 which is also found in the Bala series, is abundant ; and to this may be added 

 many other species of Orthis, which that series contains. ] 



6. Then follows, in the ascending section, a great series of beds 

 full of fossils, and these beds alternate with bands of cotempo- 

 raneous porphyry, schaalstein, &c. 



7. Lastly, there is a well-defined thick group, whose width, 

 measured transversely to the strike, is about a mile. It is com- 

 posed of calcareous slates, and contains two bands of limestone, 

 both of which have been worked for lime. It passes upwards into 

 pale-coloured earthy slates (d), and these seem to pass, without a 

 break, into the overlying Denbigh flagstone (c), which just appears 

 on the southern bank of the Ceiriog, and extends northward from 

 that river towards the vale of the Dee. The fossils both of para- 

 graphs 5 and 6, are entered in the .list of the Ceiriog fossils. 



