APPENDIX. 341 



It appears from the above tabular statement, — 



(1.) That those limestone strata which are the thickest, are situated at or near the bottom of the 

 basin ; and that the thinnest are in the middle of the basin, or about half-way down from the top. 



(2.) That those limestones which vary least in thickness, are situated about the middle of the basin ; — 

 and that the amount of their variation over the entire district, does not exceed a few inches. 



(3.) That those limestones which vary most in thickness are situated at or near the very bottom of 

 the basin ; and that the amount of variation is so great, as that in some parts the same stratum attains 

 a thickness six times greater than that which it possesses in other parts. 



(4.) That whilst those lower limestones indicate a great increase of thickness as they approach the 

 Lammermuir and Pentland Hills, — the upper limestones (being far from hills,) indicate no tendency 

 to thicken in any particular direction. 



This inference is an important one, and therefore requires an attentive examination of the above 

 statistical details. It is apprehended that they fully warrant that inference. 



It may be thought that the Burdiehouse limestone, which is stated in the table as occurring at 

 Carlops, and being so much thinner there, — is inconsistent with this inference. Independently of the 

 doubt, whether the particular limestone at Carlops now referred to, is really the Burdiehouse bed, I may 

 observe that the fact of this stratum being as near the hills at the one place as at the other, would be a 

 sufficient answer to the objection. Another is suggested by the consideration, that there may have been 

 a greater supply of sedimentary matter at Burdiehouse than there was at Carlops ; — and it has been else- 

 where explained, that there is an essential difference between the origin and formation of the Burdie- 

 house limestone, and that of all the other limestones lying over it. 



It will be obvious, that the correctness of the above inferences would be by no means impugned, — 

 though mistakes should be discovered in the table, as to the particular ^foce* where the lower limestones 

 exist. For the^ all indiscriminately shew the same tendency to thicken as they approach the hills. 



Before concluding my extracts from, and remarks on the table of coal and lime strata, I may men- 

 tion, that attempts have been sometimes made, to calculate the quantity of coal existing in particular dis- 

 tricts, and thus to anticipate the period of its total exhaustion. These calculations are necessarily very 

 vague and uncertain, — arising chiefly from the impossibility of knowing, whether the coal is in pre- 

 cisely the same condition in the unexplored parts of the basin, as it is in those places where it is worked. 

 But any calculations, however imperfect, afford some degree of approximation to the truth, — which 

 cannot mislead if viewed only as an approximation. 



From the tabular chart of coal-seams above referred to, it appears, that if all those that are worked 

 or workable, with several too thin to be worked, are taken into account, — there would be a total thickness 

 of coal amounting to 188 feet. This statement, I observe, coincides pretty nearly with an estimate 

 made by Mr Bald. He has very lately calculated the quantity of coal in the Marquis of Abercorn's 

 estate at Easter Duddingstone, — through which the two lower series of coals run. The lowest he calls 

 the Duddingstone Group,_comprising all between the " North Greens" and the " Wood Coal ;"— the 

 middle series he calls the Joppa Group,— comprising all above the Wood Coal, as far up as the " Golden" 

 Coal ;— the uppermost series in the basin, he denominates the Brunstain Group. The two former groups, 

 Mr Bald calculates, contiins (in the Marquis of Abercorn's estate) a total thickness of 108 feet. I 

 observe from my tabular chart, that the uppermost series presents an average total thickness of 75 feet,— 

 which, added to Mr Bald's estimate of the total thickness of the other two, would make the thickness 

 of coal in the entire basin 183 feet,— being only 5 feet less than the result of my own calculations. 



Let it be assumed, then, that the thickness of all the known workable seams is 1 83 feet. If there 

 was one coal-seam of this thickness, it would be easy, after marking on a map the line of its outcrop, 

 to calculate the extent of it, and the quantity of coal contained in it. But where this thickness is made up 

 by seams, some of which are at the very bottom of the basin, and the others at the top, in consequence 



