338 



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

 Thickness of " North Gbeens" in Tyne Basin. 



These general statements are useful, as they serve to shew in what parts of the district, the vege- 

 table materials from which the coal-seams were formed, the different coal-seams were most accumulated ; — 

 and where, on the other hand, they were more scantily supplied. On reviewing the above extracts, 

 it is seen, that the two coal-seams to which they refer, are thickest at or near a line drawn from Gilmerton 

 to the south of Tranent, and that towards the southern limits of the district these coal-seams thin away 

 till they cease altogether, or at least become so thin as to be unworkable. This inference is confirmed, 

 by an examination of all the other coal-seams, recorded in the tabular chart above referred to. 



It is interesting to mark, not merely the variations in the general thickness of the coal-seams in 

 ditferent parts of the district, but also the variations in the nature and thickness of the bands which com- 

 pose the seam. It is not so easy to procure information, so minute and precise as that now alluded to ; — 

 and therefore it is, that the following table is less extensive than those above quoted. But it is never- 

 theless sufficient to afford an insight into a very interesting subject. 



The analysis which has now been given of the two principal coal-seams in the district, shews, that 

 they are not homogeneous in their composition, but that they consist, or are made up of layers, the mate- 

 rials of which are extremely different. It is evident also from the nature of these materials, that they 

 could not have been deposited and spread out over the district simultaneously. The several layers or 

 bands of shale, sandstone, clay, and vegetables, must have been deposited separately and successively, so 

 that, in fact, an ordinary coal-seam, when analysed, presents a miniature section of the various strata 

 which compose an entire coal-field. This analogy holds true, in yet another respect. Not only does 

 it appear, that the bands composing the coal-seams have been separately and successively deposit- 

 ed, — but moreover the causes which brought about this deposition, must have operated over extensive 

 areas, — and been subjected to little or no disturbance. The fact, that bands of shale, not more than a 

 few inches thick, scarcely vary in thickness, over an area several miles in extent, shews an almost incre- 

 dible degree of stillness and placidity in the carboniferous waters. Any variation in thickness which they 

 do exhibit, must have arisen, generally speaking, not from disturbing causes, but from a variation in the 

 supply of sediment ; — and hence we see, that the bands characterizing particular coal-seams get thinner 

 in some places, and entirely disappear in others. 



