16 ME. PHILIP LAKE ON THE DENBIGHSHIRE [Feb. 1 895, 



noticed by several geologists since the time of Bowman, and contain 

 many fossils. They will be again referred to, and the only point 

 which it is necessary to notice at present is that they appear to be 

 considerably higher in the series than the Leintwardinensis-be&s. 



V. Detailed Description of the Beds. 



Now that the order of succession among these rocks has been 

 established, it will be possible to enter into more detail concerning 

 the character of the subdivisions and of their included fossils. 



Pen-y-glog Slates. 



The lowest beds of the Pen-y-glog Slates are seen in some heaps 

 of debris which lie immediately west of the main waste-heaps of the 

 Penarth slate-quarry. They are very shaly in character and very 

 deeply weathered, presenting a dull and earthy appearance. Occa- 

 sionally a piece may be found which is not weathered quite to the 

 centre, and then it appears that the original colour was a dark blue, 

 not unlike that of the higher beds of these slates. Graptolites are 

 common and well-preserved, the following species occurring : — 

 Monograptus priodon, Bronn, M. personatus, Tullb., M. vomerinus, 

 Mch., Betiolites Q-einitzianus, Barr., and Cyrtograptus Murchisonit, 

 Carr. 1 



The same slates are exposed in the stream which runs a little east 

 of Tomen-y-meirw ~ • and here their relations to the Tarannon 

 Shales are clearly seen in a little gorge north of the Glyndyfrdwy 

 and Gryn Ceiriog road. There is a gradual passage, and the dark 

 shales are interbedded with the pale shales of the Tarannon along 

 the boundary-line. I did not, however, succeed in finding the 

 characteristic graptolites, probably owing to the dampness of the 

 rocks. 



Outside our area, but within the Llangollen basin, the same 

 slates are well exposed on the western side of Caer Drewyn, near 

 Corwen, and on the eastern flanks of Moel-y-f aen, by the side of the 

 direct road from Llangollen to Buthin through Pentredwfr, about 

 1 mile north of Pentredwfr. In both places they lie immediately 

 above the Tarannon Shales ; in both places, too, they contain 

 Monograptus personatus and Retiolites Geinitzianus, and present the 

 deeply weathered appearance characteristic of them at Pen-y-glog. 



The slates of the Penarth quarry itself, which lie above these, are 

 well cleaved, dark banded slates which occasionally contain pyrites 

 and bands of anthracite. The fossils which have been found in 

 them are the following 3 : — 



1 These forms were collected by Mr. T. T. Groom and myself, and were 

 kindly named for us by Mr. J. E. Marr. 



2 This is an ancient tumulus, 3 miles south of Glyndyfrdwy, and about 2£ 

 miles due west of Llansaintffraid Glyn Ceiriog. 



3 This list is based on a list of graptolites collected by Dr. Hicks and 

 named by Prof. Lapworth (Quart. Journ. Geol. Soc. vol. xxxvii. 1881, p. 488, 

 footnote) ; on Marr (op. cit. vol. xxxvi. 1880, p. 283) ; on Hicks (op. cit. 



