Vol. 51.] DENBIGHSHIRE SERIES OE SOUTH DENBIGHSHIRE. 



2. The Denbighshire Series of South Denbighshire. By Philip 

 Lake, Esq., M.A., F.G.S. (Read November 7th, 1894.) 



Contents. 



Page 



I. Introduction 9 



II. Literature 9 



III. Description of the Area 11 



IV. The General Sequence 12 



V. Detailed Description of the Beds 16 



VI. Correlation with other Areas 20 



VII. Conclusion 22 



Map 13 



I. Introduction. 



There are few series of rocks in the southern half of Great Britain 

 which have been so much neglected by geologists as the Denbigh- 

 shire Grits and Flags ; and the reason is not far to seek. As a rule, 

 these rocks form rounded hills which are often completely covered 

 with heather, and there are many square miles of country without a 

 single exposure. The beds are frequently much folded and faulted, 

 and it is often a work of great difficulty to make out their relations 

 to each other. Fossils are by no means common, except in a few 

 localities ; and the most important are graptolites, which the earlier 

 geologists considered to be of little value for stratigraphical purposes. 

 Under such circumstances it is not surprising that these rocks have 

 tempted few geologists to enter the field, and that the observations 

 which have been made on them have in general been somewhat 

 cursory. 



The series, nevertheless, deserves more than a passing notice. It 

 belongs to one of the most widely-spread facies of the Silurian in 

 Britain ; and now that the stratigraphical value of graptolites is so 

 generally recognized, it has become a matter of some interest to see 

 how far these graptolite-bearing deposits correspond with those of 

 other regions. 



The area over which my observations have extended includes the 

 whole of what may be called the Llangollen basin ; but the present 

 paper is occupied chiefly with that part in which the beds are best 

 exposed and in which the succession is clearest — that is to say, 

 the south-western quarter of the basin. 



II. Literature. 



It was in 1840-41 that J. E. Bowman x published the first account 

 of the Silurian rocks of the Vale of Llangollen. In the main his 

 description is tolerably accurate, but he does not appear to recognize 

 that the flaggy beds overlie the slates [Pen-y-glog Slates] which are 



1 Brit. Assoc. Eep. of Sects. 1840 (Glasgow), p. 100 ; ibid. 1841 (Plymouth), 

 p. 59 ; Trans. Manchester Geol. Soc, vol. i. (1841) p. 194. 



