WENLOCK SERIES. 93 



certain Grits above, he refers to the Denbighshire Flag- and Grit- 

 series.' Mr. J. E, Marr places the Penyglog Flags at the base of 

 this series. (See p. 95.) In the upper part of the Clwyd Valley, 

 near Glynbach, Prof. Hughes has noted the following succession 

 of beds beneath the representatives of the Coniston Flags and 

 Denbighshire Grits:'* — 



/ Wavy-banded Sandstone \ -p 1 ci f a 



arannon 1 rale Slates. f ^ ^ ,. . 



r. • < e J . / Ciraptolitic 



Series. J Sandstones. I i\t 1 . 



Pale Slates with Graptolites {Monograptus). 



Mudstones. 



In the area of the Breidden Hills, between Welshpool and 

 Shrewsbury, the purple shales which overlie the Pentamerus-beds 

 are about 200 feet thick. ^ The Tarannon Shales have been noted 

 in the Dee Valley, and there, according to Mr. Marr, they are more 

 cleaved than is usually the case with the corresponding beds of the 

 Lake District.* 



Slates belonging to this group have been worked in some 

 localities. 



WENLOCK SERIES. 



The Wenlock Series is divided as follows : — 



X. Wenlock Limestone. ) -n* u- u i,- r^ -^ 



1157 1 1 cu 1 f Denbighshire Grits. 



2. Wenlock Shale. 



I. Woolhope Beds. 



Denbi2-hshire Flaffs. 



The term Wenlock Series, used by Murchison in 1833, is derived 

 from Wenlock Edge, in Shropshire. 



DENBIGHSHIRE GRITS AND FLAGS. 



Under the name Denbighshire Sandstones these beds were 

 described in 1841 by J. E. Bowman; later on their position was 

 determined by Sedgwick. The name is derived from the develop- 

 ment of the beds in Denbighshire. 



This formation consists of a series of shales, flagstones, sand- 

 stones, and grits, attaining a maximum thickness of at least 3000 

 feet. According to Sir A. C. Ramsay, they form but a local variety 

 of the Wenlock Series ; and apparently, where the grits thin 

 away and disappear, instead of being overlapped by the shale, they 



^ Q. J. xxxiii, 209. 



* Q. J. XXXV. 697. 



3 W. W. Watts, Q. J. xli. 539. 



* Q. J. xxxvi. 282. 



