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



bonic acid, and cause a precipitate of carbonate of iron, among tbe sediment accu- 

 mulating in tliese pai-ts. 



With regard to tlie som-ce from which the ingredients of the coal strata were 

 derived, it is impossible to say any thing, without more extended observation. 

 It certainly is a very remarkable circvnnstance, that all the coal-seams should 

 be thickest in the north part of the district, and that they should all thin away 

 towards the south ; nay, that some of them should entirely disappear before they 

 reach that limit. It is not an unfair conclusion from this fact, to hold, that 

 there must have been a larger supply of vegetable matter in the north than in 

 any other part of the district ; and if this be so, it would seem to be a corollary, 

 that the dry land which supplied, if not all, at least the largest quantity of ve- 

 getable matter, was also towards the north. I have already observed, that, 

 judging from the accumulations of sandy sediment in the district, there was pro- 

 bably dry land to the N. and NW. Moreover, if it be true (and it does seem 

 extremely probable) that the Fife coals form part of the same deposit to which 

 the Lothian coals belonged, the theory now suggested receives strong confirma- 

 tion ; because there the coal-seams are still tliicker than at GUmerton, Niddry, 

 and Wallyford. Mr Land ale, in his valuable paper on the Fife coal-field, states, 

 that one of the coal-seams at Dysart is 21 feet thick, and that there are three 

 others, each of which exceeds 10 feet in thickness. In Mid-Lothian, the thickest 

 seam is 14 feet thick ; and the next in point of thickness is less than 10 feet. 



There is still another subject connected with the origin of these several 

 strata deserving of attention. How have the elements that compose them been 

 transported? Have they been transported by means of rivers? This notion 

 does not appeal- inconsistent with the conditions presented by the shales and 

 sandstones , and, on the contrary, it is absolutely necessary, in order to answer 

 some of these conditions, implying, as they do, the existence of powerful currents. 

 How else could the enormous trees found in the Craigleitli sandstone, at New 

 Craighall, and at the Roman Camp, have been transported ? Trees of such weight 

 and size could not have been carried off from their native sites except by an 

 agent of considerable power; and it is worthy of remark, that the strata in 

 which they have been found, are invariably sandstone, which, as already re- 

 marked, indicates generally the prevalence of agitated waters. In what manner 

 the supposed rivers became charged with such accumulations of sedimentary 

 matter, and loaded with the spoils of primeval forests, it is difficult to imagine, — 

 except on the assumption, that, by occasional, or periodical inundations, they 

 overflowed their ordinaiy banks. 



It is not quite so easy to conceive in what manner the Tegetables that com- 

 pose the actual coa^-seams were collected and drifted down. We see from the 

 tables and sections of this coal-field, that it was only at particular periods. 



