98 



SILURIAN. 



of Clwyd trials for slates have been made, but owing to their bad 

 quality, the quarries have been abandoned. 



In the boring at Ware in Hertfordshire, Wenlock Shale occurred 

 beneath the Gault, at a depth of 800 feet. The proximity of 

 Silurian rocks in this area had been predicted by Prof. Hull 

 in 1861.' 



WENLOCK LIMESTONE. 



The Wenlock Limestone, so termed by Murchison from its 

 development at Wenlock Edge, consists of thick beds of concre- 

 tionary or nodular limestone of a light grey colour, containing 

 numerous fossils and separated by beds of shale. It rests conform- 

 ably upon the Wenlock Shale, and attains a thickness of about 

 300 feet. 



In parts of Wenlock Edge, near Much Wenlock, the rock is more 



Fig. 14. — Section from Ledbury to the Malvern Hills. - 

 (Prof. John Phillips.) Length about 4 miles. 



Malvern 

 Ledbury. Eastnor. Ridge-way. Obelisk. Hills. 



W E 



f^ / 



J. Lower Old Red Sandstone. 

 i. Upper Ludlow. 

 h. Aymestry Limestone. 

 g. Lower Ludlow. 

 f. Wenlock Limestone. 



3-" I' 



e. Wenlock Shale. 



d. WooUiope Reds. 



c. Upper Llandovery 

 Sandstone and 

 Consrlomerate. 



b. Hollybush Sandstone and 

 Black Shales with Olenus. 

 a. Felspathic Rocks. | p^^^^^^^_ 

 X. (jrneissic Kocks. ) 



crystalline ; and where varied colours prevail, the matrix being 

 charged with Encrinites and Corals, it forms a pretty marble, though 

 the slabs are of no great dimensions. Dull grey, dark blue, and 

 even pink varieties of this limestone are met with. At Ledbury 

 there is an oolitic limestone known as the Ledbury Marble. 



Some of the beds, consisting of impure earthy limestone and 

 shale, contain large concretionary masses of good limestone, called 

 'wool-packs' or 'hailstones': some of them near Wenlock have, 

 according to IMurchison, a diameter of 80 feet, and they are 

 quarried out, leaving large cavities. Although very thick near 

 Wenlock, the limestone thins out so rapidly in its range to the 

 south-west, that even in the interior of the Ludlow promontory it is 

 represented by thin courses made up of small concretions only, and 

 near Aymestry it is merely represented by a few concretions, vary- 

 ing in size from two inches to two feet, but still full of beautiful and 



1 Coal-fields, edit. 2 ; R. Etheridge, G. ]\Iag. 1S79, p. 2S7 ; J. E. Marr, 

 Classification of the Cambrian and Silurian Rocks, p. 72 ; J. Hopkinson, Trans. 

 Watford Nat. Hist. Soc. ii. 241. 



"^ From Horizontal Sections, Sheet 13 (Geol. Survey) ; reproduced from section 

 published by Geol. Assoc, in Programme, 1879. See Proc. G. A. vi. 235. 



