288 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



part of the Bala series. Corwen stands on the upper part of the 

 hard, dark grey Bala grits, which in this instance are very slaty. 



Proceeding from Corwen southwards, the following is the position 

 of the beds in descending order. 





Dip of Bedding. 



Dip of Cleavage. 



Immediately south of Corwen 



By the road to Bala 



Near Corwen 



N. 25° 



N.E. by N. 15° 



N. 10° 



N. 5° 

 N. 30° 



N. 63° 

 N. 55° 



Softer beds as you approach Llan- 

 drillo 



Slate of NantCwm Dywyll 





The low dip from near Corwen to Llandrillo accounts for the ex- 

 tent of surface over which the grits are spread. The lower beds, 

 which commence about three miles south of Corwen, become more 

 soft and argillaceous. They extend to about two miles south of 

 Llandrillo, that is, about six miles south of Corwen. There they 

 rest unconformably on a poor roofing-slate, which the author regards 

 as the top of the Cambrian system. The slate is quarried in Nant 

 cwm Dywyll, 2^ miles S.S.E. of Llandrillo, and at the head of Blaen 

 Iwrch, just below and east of Craig Berwyn. 



On comparing the Lower Silurian rocks south of the Dee, near 

 Llansaintfraid glyn Ceiriog, with those of the Bala district, the author 

 finds the following points of agreement between them. Taking them 

 in descending order, he finds in both series, — 



1. A dark grey roofing-slate. 



2. A series of rotten schists containing two beds of dark limestone, and full of 

 Lower Silurian fossils. 



3. Grey slaty grits, containing occasionally Lower Silurian fossils. 



With this agreement in the mineral character, in the order of su- 

 perposition, and in the organic contents of the two series of beds, 

 he holds it scarcely possible to doubt of their identity ; and espe- 

 cially he regards as fully established the identity of the two lime- 

 stones of the Ceiriog and of Bala. 



Section 1. From Llanelidan to Pistill Riiaiadr 

 (distance 12 miles — scale 5 miles = 1 inch). 



8. Carboniferous limestone. 



.■). Ludlow series. 



4. Wenlock series. 



3. Lower Silurian schists. 



1 . Cambrian schists. 



S. Slate. 



TT. Greenstone. 



