54 Mr. N. J. Winch on the Geology of 



Chalybeate springs, some of which deposit large quantities of yel- 

 low ochre, are common in every part of the Coal-field ; and a water 

 which flowed through the wooden pipes at Walker colliery, used to 

 let fall a copious precipitate of gypsum. The substance formed 

 during the twelve working hours of the mine was black, but at 

 other times was as white, and had the same degree of hardness as 

 chalk. A layer formed in twelve hours was about fV of an inch in 

 thickness. Specimens of this sediment are to be found in many 

 cabinets, but are now no longer to be procured, the high main coal 

 being there exhausted, and the colliery laid in. 



The choak damp, the fire damp, and the after damp or stythe, are 

 the miner's terms for the gases with which the coal mines are 

 affected ; and of these the second both from its immediate violence 

 and as occasioning the other kinds of damps is the most to be 

 dreaded. The accidents arising from it have become more common 

 of late years, but it should not for a moment be supposed that they 

 arise from any want of skill or attention in the professional surveyors 

 of the mines. The following seem to be the causes in which the 

 gas originates. 



1st. The coal appears to part with a portion of carburetted 

 hydrogene, when newly exposed to the atmosphere ; a fact rendered 

 probable by the well known circumstance of the coal being more 

 inflammable when fresh from the pit than after long exposure to the 

 air. 2d. The pyritous shales that form the floors of the coal-seams 

 decompose the water that lodges in them, and this process is con- 

 stantly operating on a great scale in the extensive wastes of old 

 mines. In whatever mode we suppose ihe gas to be generated, it 

 is disengaged abundantly from the High Main, but more particularly 

 from the Low Main coal-seam, and that in a quantity and with a 

 rapidity that are surprising, it is well known that the gas frequently 



