SALTER — A CHRISTMAS -LECTURE ON COAL. 



G3 



from the surface, a, a, runs down the porous strata, till it comes to 

 the bottom of the basin, and there 4 finds its own level. It will not run 

 through the clay (b), and hence you have only to drain what lies 

 above it in the strata, a. Nay more, if one part of the basin be cut 



Sandstone. 



c - 



Clay. b 



Fig. 4.— Section of Coal Basin. 

 a, porous beds ; b, clay ; c, water level. 



off from the rest by faults, as in our diagram, p. 9, only what lies 

 on its own side of the fault will have to be drained by any shaft. 

 So that a fault is a positive advantage, paradoxical as it may sound. 



Though they cut up, and often tumble the beds much, yet being filled 

 with clay, they effectually shut off the water of one compartment from 

 the other ; and render it possible to work in the dry, when otherwise 

 you would have to work in the wet. Like many other apparent dis- 

 advantages, they do good after all. 



We may guess what a terrible plague the water is to the miner, 

 when we know that in sinking some shafts, the engine has had to draw 

 off three thousand gallons a minute, with a pump eighteen inches 

 diameter. It is still worse in the Cornish tin mines. 



It is a curious fact that in deep mines the water is generally salt — 

 often Salter than the sea. It often, too, contains green vitriol (sulphate 

 of iron) iodine, bromine, and other constituents of sea-water, which no 

 doubt it once was. We shall see that by and bye. 



And now we've got our shaft down to the lowest point — our pumps 

 at work — nearly all our money spent ; and we have to find out how 

 to work the pit to the best advantage : for some pits will send up three 

 hundred or four hundred tons a day; and an acre of coal with sixteen 

 thousand tons in it may be cleared off, by a good method of working, 

 in six weeks ! 



The winding engine o? " whimsey" is not nearly so powerful as the 

 pumping engine — seldom one hundred horse power — and round the 

 drum over the pit's mouth are coiled the flat chains (of three or four 

 links,) or strong ropes, which last they find best for drawing coal. 



The baskets or " skips" are of various shapes in different mines. 

 A common form, which strikes a stranger with some surprise, is a low 

 flat box on wheels, on which the coal is piled ; and when the pile is 

 high enough, abroad iron hoop is thrown over it; more coal is added; 

 other hoops thrown over that — till the pile is as high as can be raised 



