WENLOCK SERIES, 97 



Fenestclla, Siomafopora, Ceriopora, and Thamnisctis} Fossils have 

 been found at Castel Dinas Bran. 



In Shropshire, as stated by Mr. G. Maw, there is an insensible 

 gradation between the Wenlock Limestone and the Wenlock Shale, 

 the shales under the limestone containing scattered concretionary 

 courses of nodular limestone. Mr. Maw has termed this inter- 

 mediate zone the Tichvood Beds, which may be roughly estimated 

 at from 300 to 500 feet in thickness. The beds are exposed in the 

 deep road-cutting near the railway bridge between Tickwood and 

 Farley Dingle ; also east of Benthall Edge, opposite Ironbridge ; 

 and in the adjacent cutting on the Severn Valley Railway : they 

 are highly fossiliferous. The Shales beneath would be from 1800 

 to 1900 feet in thickness, and comparatively barren in organic 

 remains ; but near the base is a fossiliferous zone of shales 80 to 

 100 feet in thickness, termed the Buihhvas Bah. These beds are 

 exposed on the east bank of the Severn, a short distance above 

 Buildwas Bridge ; also south of Harley. The portions of the 

 Wenlock shales above these Buildwas Beds, and below the Tick- 

 wood Beds, being the barren shales of Coalbrook Dale and Ape 

 Dale, HOC to 1200 feet in thickness, are termed the Coalbrook 

 Dale Beds ; and the beds below the Buildwas Beds, the barren 

 shales of Buildwas Park, 500 to 600 feet in thickness, are termed 

 the "Basement Beds." We have thus the following local divisions:^ — 



Upper — Tickwood Beds. 

 Middle — Coalbrook Dale Beds. 



( Buildwas Beds. 



( Basement Beds. 



In North Wales the Wenlock Shales are developed between 

 Conway and Abergele, and here they are overlaid by the basement 

 beds of the Carboniferous System — a structure which represents 

 one of the greatest unconformities in the British Isles. ^ They 

 occur near Llangollen, Welshpool, Montgomery,^ and Builth, 

 and as far south as Llanarthney, between Llandeilo and Caermar- 

 then. From Wenlock Edge they extend towards Presteign and 

 New Radnor. In the Woolhope district the beds may also be 

 studied. (See Fig. 13.) At Malvern, the Wenlock Shale, consisting 

 of dark blue or grey sandy shale, with thin bands of limestone- 

 nodules, is estimated by Prof. Phillips to have a thickness of 640 

 feet. (See Fig. 14.) On the east side of May Hill the beds have 

 been well exposed, and numerous fossils have been obtained. 

 They have also been exposed in many places in the Usk district, 

 and also to the west of Tortworth, in Gloucestershire. (See Fig. 12.) 



In the Llangollen country the Wenlock Shale has been worked 

 for roofing slates in the Valley of Glyn Ceiriog.^ In the Vale 



^ Q. J. xxxviii. 44, 377. 



^ T. Davidson and G. Maw, Geol. Mag. 1881, p. 103 ; T. Davidson, Silurian 

 Brachiopoda, vol. v. (Supplement), p. 71. 



^ See A. Strahan, Geology of Rhyl, etc. (Geol. Survey). 



* See W. W. Watts, Q. J. xli. 536. 



* Symonds, Records of the Rocks, p. 170. 



Wenlock Shales 



Lower 



