Geologt/ of Coalbrook Dale. 421 



conchoidal. The masses which constitute the strata frequently form large, 

 irregularly-rounded blocks, h'gh'y crystalline and pure. They are termed 

 "hailstones," and form an excellent flux for the ironstone. The lower strata 

 of this limestone are well exposed in the numerous quarries along Benthall 

 Edge and at Lincoln Hill. Their colour is dark bluish gray, and their texture 

 is more earthy than the central strata, which are also much thicker bedded. 

 Strongly-defined lines of cleavage or joints traverse this limestone ; and are 

 well exhibited in the quarries at Benthall Edge, one set ranging nearly at 

 right angles to the strike of the rock, and the other almost parallel to it. The 

 direction of the first is nearly true north and south ; that of the second about 

 12° S. of west and 12° N. of east. At the " Vineyards," (half a mile further 

 westward,) where the strike is a few degrees more south, the direction of the 

 joints is still the same. At Gleedon Hill, they hold a similar course, whilst 

 the dip is 12° north ; but, at Bradley, intermediate between these two places, 

 the dip is about 8° W.S.W., and the cleavage is apparently nearly N.W. and 

 S.E. This district is, however, so much disturbed, that it is difficult to arrive 

 at any certain conclusion. 



Mineralogical Contents. — In the Wenlock limestone, there are no ores in sufficient quantity to 

 repay the working. Crystallized carbonate of lime occurs in the seams and partings of the strata, 

 frequently forming beautiful rhombic, tetrahedral, and hexahedral crystals. Flesh-coloured sul- 

 phate of barytas, splitting into rhombic crystals, is common in the fissures of the limestone at 

 Benthall Edge. Small crystals of sulphate of copper are occasionally disseminated upon the cry- 

 stals of carbonate of lime ; and the sulphurets of iron, copper, and lead are met with in small lumps 

 and in thin filaments in the lower part of the limestone. The peroxide of manganese also occa- 

 sionally fills up small cavities and fissures in the rock. In the central beds are sometimes found 

 geodes of a very pure limestone, the cavities of which are lined with beautiful crystals of calca- 

 reous spar. 



Organic Remains of the Wenlock Limestone. 

 Fossils abound in this formation, and are in general extremely well pre- 

 served, especially the corals which are found in the central limestone at 

 Gleedon Hill. In that portion of the formation are beds, sometimes more 

 than 20 feet thick, composed almost entirely of remains of Crinoidea, of white 

 and pink colours, the limestone thereby acquiring a curious, speckled appear- 

 ance. The substance of the corals is frequently replaced also by a pure, semi- 

 transparent pinkish carbonate of lime, which has beautifully preserved the 

 most delicate internal structure. In the lower beds, Crinoidea are much less 

 numerous, occurring only in detached fragments between the strata ; but 

 they contain great abundance of Favosites, and several species of Eumophalus, 

 Leptaena, and Pleurotomaria. In the uppermost beds organic remains are less 

 abundant than in the middle or lowest, and are almost entirely confined to 

 Testacea. 



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