Lower transition LtMEStONE. 



89 



tion. The dotted line and open spaces show where the limestone 

 has been quarried away: 1,2, are deep galleries over each other, 

 along which the limestone is also quarried ; the lower is near the 

 level of a canal which penetrates the hill to convey the limestone 

 away : c, represents the outcrop of the thirty feet bed of Stafford- 

 shire coal, which comes to the surface near Wren's Nest Hill ; b, 

 represents the arrangement of the limestone strata at Dudley Castle 

 Hill, similar to that at Wren's Nest Hill ; and d, a hill capped with 

 rudely columnar basalt in the vicinity. In this section the proportion 

 of distance has been disregarded, in order to comprise the different 

 objects in one view : the distance between Dudley Castle Hill and 

 Wren's Nest Hill, is about two miles. The strata at Dudley Castle 

 are what is called saddle shaped, declining on each side of the hill. 



The transition limestone of Dudley is not covered by any beds of ' 

 the upper-transition or mountain limestone, but by strata about sev- 

 enty-six yards in total thickness, composed of imperfect limestone 

 and sandstone, which separate it from the lowest coal measures. It 

 is therefore to be particularly noticed, that the coal strata, which in 

 most of the coal districts in England rest upon the upper transition 

 or mountain limestone, in this part of Staffordshire, rest upon the 

 lower transition limestone. The remarkable fossil, the trilobite, call- 

 ed the Dudley fossil, occurs principally if not entirely, in a stratum 

 under the first limestone. There are shells in what are called the > 

 wild measures, but they are in a soft and decomposing state. 



The lower transition limestone in England and Wales, is not a 

 very extensive formation : it skirts the granite of Dartmoor, and 

 part of the Malvern Hills ; it extends in a narrow belt from Wen- 

 lock, in Shropshire, to Caermarthen, in Wales, and is generally oc- 

 companied with soft greenish schistose strata, called dye earth, which 

 contain numerous impressions of shells. A few patches of this lime- 

 stone occur in various parts of the slate districts in Wales, and Cum- 

 berland. This part of the transition limestone series is remarkable 

 chiefly for its organic remains ; it is rarely metalliferous. 



The upper transition or mountain limestone is, as I have before 

 stated, the limestone to which the French geologists gave, par excel- 

 lence, the name of Calcaire de transition. It is by many English 

 geologists considered as a distinct formation from the lower, or what 

 they call the true transition limestone ; and it is said to be "separated 

 from it by the important formation of the old red sandstone :" but 

 the latter is only a variety of greywacke, and is acknowledged, even 

 by those who make it a distinct formation, to graduate into grey- 

 wacke, and to possess all the general characters of that rock, except 

 that it is colored red. The old red sandstone contains, in some sit- 

 uations, beds of imperfect limestone, which may be said to connect 

 the lower transition and mountain limestones in one formation, to- 

 gether with the associated beds of greywacke, red sandstone, and 

 gritstone. 



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