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



It is veiy remarkable to observe the different proportions of hydrogen in 

 these several kinds of coal. It is enough for my present purpose to shew, by 

 reference to the elements as weU as the crystalline structure of coal, that each 

 vai'iety is perfectly different in its constitution and organization. 



Now, how is this difference to be accounted for ? Will it be said that it 

 may have been occasioned by differences in the character of the vegetables which 

 compose the coal ? This notion was lately started by Mr Hutton of Newcastle, — 

 and nothing is more likely. But these different vegetables were of course not ori- 

 ginally deposited, in separate layers. They must all have been blended together, 

 when they settled down and formed a pulpy deposit, at the bottom of the estuary 

 in which they had been floating. How, then, did they afterwards come to sepa- 

 rate into distinct seams ? What agent put the elements of the vegetable mass 

 in motion, so as to make them form new combinations ? Would subterranean 

 heat have that effect ? On this subject, it would be very desirable to have ex- 

 periments to refer to, instead of having to offer merely explanations which are 

 httle better than conjectures. At the same time, there are many cu'cum!5tances 

 which a priori support the view just thi-own out. We know that, shortly after 

 the period when these carboniferous strata were deposited, there was a great evo- 

 lution of subterranean heat ; and it is impossible to doubt, that in rising up 

 through the sedimentary strata, it would effect important changes in their or- 

 ganization and structure. For example, it would cause them to contract in 

 size or volume, by expelUng from them much of the water mth which they 

 were impregnated ; and they would not contract, without having cracks and 

 fissures formed in them, whereby they would of course acquire the outlines of a 

 rude crystallization. Moreover, the same agent may explain the formation in 

 these fissures, of the veins of carbonate of lime, u-on, and magnesia, described 

 in the first part of this memou\ I have ah'eady aUuded to the great proba^ 

 bility, that, at this period, the sea in which these strata were deposited, held 

 many of these substances in chemical solution, — as it still holds some of them, 

 to a small extent. In that case, the immediate effect would be, whenever heat 

 reached the vegetaljle deposit, to expel a portion of the carbonic acid, ])erhaps 

 also to evaporate a portion of the water which was previously in the fissures ; 

 and thus leave in them films of cai-bonate of lime, iron, and magnesia. 



I need hardly add, that the views now thrown out, would explain the occur- 



• In the Appendix F, will be found a statement of some experiments recently made, which shew 

 how various are the proportions of hydrogen in different kinds of even the same sort of coal, viz. parrot- 

 coal. 



