Vol. 51.] SERIES OF SOUTH DENBIGHSHIRE. 11 



base of the Denbighshire Grits near Corwen, Dr. H. Hicks T gives a 

 section across onr area. He refers the Pen-y-glog Slates and appa- 

 rently the gritty beds above them to the Upper Llandovery, and 

 places in the Wenlock only the higher slaty beds above the grits — 

 in his section the slates of Moel Morfydd. The graptolitic fauna 

 of the Pen-y-glog Slates and their position above the Tarannon 

 Shales are sufficient to show that this correlation caDnot be accepted 

 in full. 



[Since this paper was read, my attention has been drawn to the 

 account of the geology of North Wales given by Dr. Hicks in the 

 ' Explication des Excursions ' of the International Geological Con- 

 gress at London in 1888, in which he states that the upper beds of 

 the North Welsh Silurian, visible at Dinas Bran and Moel Morfydd, 

 may probably be referred to the Ludlow. 2 — Nov. 22nd, 1894.] 



There are no further notices to record : and it will thus be appa- 

 rent that the Denbighshire series of this area has received but 

 scanty attention from geologists, and that little has been added to 

 the old descriptions of Bowman and Sedgwick. Farther north, 

 however, in the Vale of Clwyd, the series has been examined in 

 detail by Prof. Hughes. 3 He recognizes the Pen-y-glog Slate 

 and the Pen-y-glog Grit, already noticed in the Dee Valley. The 

 grit is succeeded by a great thickness of flags which he calls tho 

 Nantglyn Plags, and which are characterized by Orthoceratites, 

 Actinacrinus, etc. ; and these are followed by a series of more gritty 

 beds, in one subdivision of which he finds Acidaspis HugJiesi, 

 Salter, MS. This species occurs in the Coniston Grits of the Lake 

 District, but is also recorded from other horizons. Prof. Hughes 

 refers a part of the upper gritty beds of the Clwyd to the Ludlow, 

 and the beds below to the Wenlock. It will be seen subsequently 

 that the correspondence between this succession and that of the Dee 

 Valley is extremely close. 



III. Description oe the Area. 



The Denbighshire series of the southern part of Denbighshire 

 forms an incomplete basin which lies between the Bala rocks of 

 Cyrn-y-brain on the north and those of the Berwyns on the south, 

 and which extends from the Nant Morwynion fault on the west till 

 it is covered in the east by the Carboniferous rocks of the North 

 Wales coal-field. In the portion of this basin which lies north of 

 the Dee the beds are greatly folded and cut up by faults ; but in 

 the part which lies south of that river, the faults are few, and the 

 dip of the beds is low and very regular. It is the western portion 

 of this southern half which will now be described. Here the 

 rocks are comparatively well exposed, and the sequence can be 

 determined without much difficulty. 



1 Quart, Journ. Geol. Soc. vol. xxxvii. (1881) p. 482. 



2 Congr. Geol. Intern. 4™ Sess., Compte-rendu, London, 1888, p. 286. 



3 Quart. Journ. Geol. Soc. vol. xxxv. (1879) p. 694; Proc. Chester Soc. Nat. 

 Sci. & Lit, no. 3 (1885) p. 8, pt. iv. (1893) p. 141. 



