250 ON THE GEOLOGY AND MINING OF 



and becoming of considerable magnitude towards the south-west, 

 and cropping out and losing themselves on the north-east side. 



The lecturer then proceeded to describe in succession, the valua- 

 ble deposits and the mode of working them in different situations. 

 Of the limestone, two beds, of twelve or fourteen yards thick appear 

 to prevail beneath the coal formation It is of the period termed 

 by Buckland transition, and abounds in the forms of Trilobites, 

 Encrinites, and a variety of Crustacea and Zoophytes. It appears 

 at the surface near Walsall ; forms a range of considerable hills 

 from Sedgely to Dudley, and is again seen at the Hayes, near 

 Stourbridge. Its elevation and its excavated quarries afford many 

 strikingly picturesque points of view, which were illustrated by 

 large drawings ; one of which, presenting the present aspect of the 

 Wren's Nest, was adapted, by a removable piece, to exhibit a sec- 

 tion of the hill, shewing the workings of the strata, their position, 

 and the line of subterraneous canal constructed by the proprietor 

 for facilitating the transit of the heavy material. The limestone is 

 detached from its bed by the gunpowder blast, and is, in some situ- 

 ations, worked, like coal, by means of deep pits or shafts. 



Above the lime, at a considerable distance, lie the Coal Measures, 

 of which the following table gives the total thickness of the gelable 

 beds, or those which pay for working : — 



Y. FT. IN. 



Brooch coal 10 9 



Thick coal 10 



Heathen coal 1 



New mine 8 2 3 



Yards 21 



Of these, the most important is generally known by the descrip- 

 tive title of " Ten Yard Coal." This is composed of numerous 

 beds of varying qualities, separated by thin " partings" of sand or 

 clay, and it is worked by the miner in five or six sections or stages, 

 commencing with the lowest ; large quantities, however, are left in 

 the mine, as pillars for supporting the roof, and as heaps of unsale- 

 able slack. 



The thinner beds are more nearly cleared away ; the superin- 

 cumbent earth being supported by conical pillars, or " cogs," of 

 refuse and waste. In all cases, a series of small passages for venti- 

 lation, called " air-heads," is carefully formed : these follow the en- 



