MR MILNE ON THE MID-LOTHIAN AND EAST-LOTHIAN COAL-FIELDS. 293 



rence of these substances also in all the other stratified deposits, whether in fis- 

 sures or in drusy cavities — inasmuch as all these deposits must have been satu- 

 rated with the water in which they settled down. 



Before leaving this part of the subject, let me, in a single sentence, advert to 

 the origin of the hydrogen which forms so important an ingredient in most coals. 

 I say in most coals, for it does not exist in all kinds of coal. For example, an- 

 thracite or Kilkenny coal wants it entirely. It exists, however, in all the varie- 

 ties of coal which occur in the Lothians, and in the proportions previously stated. 

 This gas is the carburetted hydrogen, which in some collieries proves so fatal by 

 explosions, and is called " fire-damp" by the miners. Some suppose that it is 

 generated in old wastes by the decomposition of water, the hydrogen of which 

 unites with the carbon of the coal. But it has recently been discovered by Mr 

 HuTTON of Newcastle, that the gas exists in the substance of the coal itself, 

 being contained in small cells, only discoverable by the microscope. He is of 

 opinion, that it may exist in these cells even in a liquid form, in consequence of 

 the great pressure to which it is subjected. It is in this way that the blasts are 

 accounted for, which occasionally take place in the English and Ayrshire col- 

 lieries ; — for by the working of the coal, the pressure is removed, and the hydrogen 

 immediately passes from a liquid into a gaseous form. 



Hydrogen gas is therefore an original constituent element or ingredient, of 

 the coal strata in which it occurs ; and it is not generated by external causes, as 

 the decomposition of water. If the latter theory were true, this gas should occur 

 in all kinds of coal, — but it does not. 



That the hydrogen gas contained in the cells of the coal has been derived 

 from the gums and resins of the vegetable matter which formed the substance of 

 the coal, is not only probable, but obviously true. But I would venture to ex- 

 press a doubt, whether the fire-damp of coal mines may not, in many cases at 

 least, come from a totally different source. It is well known that this gas is 

 evolved in many parts of the globe, where no coal exists. Farther, and what 

 is more to the point, it is evolved in this very district from subterranean sources. 

 This is the case at Prestongrange. It comes up through the fissures which in- 

 tersect the strata at that place, where they are in contact with basalt and green- 

 stone. The quantity is so considerable, that, when the coal is worked near the 

 trap-dyke, safety-lamps must be used. It is a strong corroboration of the view 

 now submitted, that in no other part of the Lothians is this gas known, at least 

 in the form of fire-damp. Whilst, on the other hand, in Fifeshire, Stirlingshire, 

 and Ayi'shire, where the strata are riddled by trap-dykes, this infiammable gas is 

 very abundant. These views suggest a possible origin for some of the hydrogen 

 gas, with which the coal itself is impregnated ; for if it was evolved in large quan- 

 tities from Nature's subterranean laboratories, before the vegetable deposits had 

 become hardened and consolidated, much of the gas might be retained by them. 



