North 



South. 



Geology of Coalhrook Dale. 435 



vegetation^ its mounds remaining- for years without a blade of grass ; whereas 

 the shale of the ballstone forms a very productive soil, and is used as a manure. 

 In the former marine, and in the latter, only vegetable remains are found. 



For further explanation of the mineralogical characters of the different 

 strata, I must refer to the explanatory sections of Woombridge pit (Appendix 

 A.) by Dr. Townson, and that of the Hill's Lane pits, Madeley, by myself 

 (Appendix). 



In the upper measures, the coal seams are usually thin, distant and irre- 

 gular in their deposition ; whereas, in the lower, they are thick and persistent 

 over the whole field. The average thickness of the principal coal-beds is 

 about 3 feet ; and the number of the seams varies from 7 to 22. The following 

 table exhibits the total thickness and number of the coal-beds at each place 

 respectively. 



Total Thickness. No. of Beds, 

 f Donnington 55 feet 19 



Woombridge 52 18 



New Hadley 46 16 



MaHnslee ZQ 15 



Dawley 43 17 



Lightmoor 40 17 



Madeley 3.3 22 



Broseley 24 10 



*- Amies 16 7 



In these localities the productive coal-measures are fully developed, and 

 consequently the difference of total thickness does not arise from the cropping 

 out at one place of beds which exist at another. The Madeley sections have 

 been so carefully made, that the thinnest layer has been recorded, which is 

 not the case elsewhere. Hence the great difference in the number of the 

 beds. We see from the above table, that the number, and especially the total 

 thickness of the coal seams, decreases to the south. The same phenomenon 

 also occurs, as will presently be shown, in the ironstone measures. 



The coals of this district are generally of the variety called slate coal. Some of the upper 

 seams, especially the fungous coal, contain a large jiroportion of mineral charcoal. Foliated coal 

 forms several of the thin upper seams, and particularly the sulphur coal, underlying the Penney- 

 stone. This coal often breaks into very regular cubical fragments, and has a brilliant lustre. 

 Cannel coal is of rare occurrence. At Madeley several tons of it were found in the middle of 

 the flint coal, forming a layer 8 inches thick, which gradually thinned out. 



Many of the coals contain so much sulphuret of iron, that they can be used only for making 

 lime, as the " sulphur coal " below the Penneystone, which is, in other respects, a fine seam. These 

 pyritous beds are called sulphur or stinking coals, and are distinguished by the lustre and sharp- 

 ness of their fracture, their greater specific gravity, and by their unpleasant odour while burning. 

 VOL. V. SECOND SERIES. 3 L 



