WENLOCK LIMESTONE (CONCRETIONARY STRUCTURE OF). 



211 



stones 1 ." Where these concretions are prevalent, the strata undulate or are contorted 

 as expressed in the preceding wood-cut. The succeeding wood-cut represents the old 

 quarries at Lincoln Hill, where the limestone was extracted by being hauled up the 

 inclined plane of the strata, and will convey some notion of these undulations or con- 

 tortions. They have, I conceive, for the most part been formed during that process 

 of solidification or crystallization which gave rise to the concretions of the limestone, 

 and cannot be considered as resulting from the dislocations by which this tract has 

 been agitated, for such concretions enter intimately into the structure of the Wenlock 

 limestone 2 . 



26. 



Old quarries at Lincoln Hill (Iron Bridge). The dark shades indicate the places from whence the concretions or ball- 

 stones have been extracted. On the right hand b are the overlying coal grits (see p. 105.). 



As we advance, from the gorge of the Severn to the south-west, the calcareous matter 

 rapidly expands (see Map), particularly near Tickwood and Gleedon, where the lime- 

 stone spreads over a width of upwards of a mile, occupying two promontories, extend- 

 ing between Wyke and Buildwas, in which much ball-stone is exposed. In one quarry 

 recently opened (called the Yell), the small concretionary beds dip on the one side to the 

 north, on the other to the south-east, and the centre of the hill consists of one massive 

 ball-stone, which when I visited the spot, was laid bare to the depth of about eighty feet! 

 the surface alone being covered with a few thin nodular beds 3 . 



1 These are much preferred as a flux for the iron ore to the other impure and argillaceous beds. 



5 Mr. Prestwich assures me, that in the deepest recesses of these limestone galleries, the undulations, being 

 at first gradual, increase with the depth, until at about eighty yards from the surface they present a series of 

 very slightly curved arches about twenty yards long, separated by rapid, step-like descents of four to six yards 

 each ; but all these lines, however curved, are unbroken. 



3 The exact width of this mass of ball-stone had not been proved when I last visited these quarries, but it is 

 doubtless very great, and must be of considerable value on account of its superior quality and accessible position. 



