74 Mr Bald on the Spontaneous emissions of Gas. 



spontaneous emission of gas ; but a cavity or excavation great- 

 ly favours its flowing from the coal, for a long mine or gallery 

 cross-cuts the fissures, and allows the gas to come off freely, 

 and in great abundance. 



Dr Thomson mentions the proximity of greenstone to the 

 spot where the coal and lime-rock of Bedlay are found. I have 

 upon this to remark, that in the coal-fields of Scotland inflam- 

 mable gas is frequently found in the coal-fields where beds of 

 greenstone abound. 



The following collieries have inflammable gas and beds of 

 greenstone in connection with the strata: — Bannockburn, Plean, 

 and Greenyards in the vicinity of Stirling ; Bo-ness, and the 

 greater part of the collieries in Ayrshire, and at Mr Hous- 

 ton's colliery of Johnston in Renfrewshire. 



It is remarkable, that in the great and extensive collieries 

 and coal-fields in Clackmannanshire, and along the whole coast 

 of Fife, inflammable gas has not been found, excepting in a 

 trifling instance at Lord Elgin's colliery, and in it greenstone 

 also abounds. Preston Island is in the county of Perth. 



Upon the south side of the Forth, with the exception of the 

 Bannockburn and Bo-ness districts, there is no inflammable gas 

 found ; and the districts free from inflammable gas comprehend 

 the very extensive coal-fields around the Carron works and 

 Falkirk, and, without exception, all the collieries in the Lo- 

 thians ; but in these collieries beds of greenstone are not found. 

 Dikes or vertical veins of this are found in several places. 



What is thus stated as to the connection with greenstone 

 and inflammable gas is not the case in every instance ; for the 

 Glasgow coal-field abounds with hydrogen gas, and there are 

 no beds of greenstone in the chief part of the field ; but they 

 very much abound in the district around the town of Airdrie, 

 and are found in the north part of the city of Glasgow, and to 

 the north-east. 



It appears that some coals throw off* inflammable gas freely, 

 while others of the same quality and constituent parts will yield 

 no gas without the application of heat — a circumstance not 

 easily accounted for, — at the same time I am led to infer, that 

 when the Scotch coals are long exposed to the action of the sun 

 and weather, much of the inflammable gas is dissipated, and this 



