WENLOCK FORMATION — (DUDLEY LIMESTONE). 



483 



measures, some coal shafts having been sunk within a few yards of the outcrop of the older rock. 

 The overlying beds, as at Sedgeley, contain the Leptama lata, together with the Cypricardia amyg- 

 dalina. The limestone quarried from the central portion of the rock differs in no respect from that 

 of Sedgeley, except that it is less abundant and of inferior quality, being still more argillaceous. It 

 does not, as far as I could observe, contain the Pentamerus Knightii, but it incloses the well-known 

 shells of the Aymestry limestone, Terebratula Wilsoiii and Pleurotomaria, with others which are 

 common to the whole of the Upper Silurian Rocks, such as Productus depressus, Atrypa aflinis, &c. 



As the strata are highly inclined, and their southern end is cut through by the high road from 

 Stourbridge to Hales Owen, a better passage is there shown, from the limestone into the lower beds 

 of the Ludlow formation, than in any other part of the district. Like the masses already described, 

 this little boss of Ludlow rocks has been thrust up through the environing coal measures, its southern 

 end advancing nearly to the edge of the Lower New Red Sandstone. 



A transverse section across it from east to west exhibits the appearance represented PJ. 37- f. 5. 



Wenlock (Dudley) Limestone. (2nd Formation of the Silurian System.) 



This second member of the Silurian System, being of infinitely greater value, has been 

 much more laid open than the upper formation or Ludlow rocks. It rises to the north 

 of Dudley in several elliptical masses, trending in parallel directions from 10° west of 

 north to 10° east of south ; the chief of which are the Wren's Nest, the Castle Hill and 

 Hurst Hill. The formation occupies a broader surface on the eastern side of the tract 

 at the town of Wallsall, which is built upon it, and to the east of which some strong 

 ridges of the limestone run along the edge of the coal-field from north-east to south- 

 west. Besides these places where it comes to day, with merely an occasional covering 

 of gravel, the limestone has been discovered by mining beneath the coal-field. 



The Wren's Nest. (See ground plan and section, p. 484 j and view, p. 485.) 



The chief mass of limestone in the district north of Dudley is at the Wren's Nest, 

 which we shall first describe, as it exhibits a full type of the formation. The solid lime- 

 stone, which is quarried, lies in two bands, separated from each other by shale, the up- 

 permost being 28 ft. 4 in., the lower 42 ft. 3 in. thick. 



These bands are divided into beds, distinguished by the workmen under the following 

 names. 



Upper or thin measures. (6. of wood-cut.) 



ft. in. 



White grey measures (left for roof) 6 0 



White grey measures 6 6 



Strong hanging stone (darkish colour) 6 4 



Top sink 2 7 



Pricking, i. e. way-board of shale (blasting layer)... 0 2 



Bottom sink 1 2 



Half yard measure 1 6 



Measure under "half yard" 1 9 



Bottom measure 2 4 



28 4 



Lower or thick measures, (d. of wood-cut.) 



ft. in. 



Grey measure (left for roof) 8 0 



Strong grey measure 4 6 



The flints 4 0 



Silks measures.. 4 0 



Second yard measures 2 2 



First yard measure 2 2 



Top sinks 1 3 



Pricking, i. e. way-board of shale (blasting layer)... 0 4 



Bottom sinks 2 4 



Black stone ... 13 0 



42 3 



