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NOTES EXPLANATORY OF THE PLATES ILLUSTRATING THE FOREGOING 



MEMOIR. 



The Map on Plate XVII. is intended not merely to represent the extent of the Coal-field described 

 in the preceding Memoir, but also to indicate the nature oi the formations skirting the coal-field. 



It should be borne in mind, however, that the strata of this coal-field reach beyond Haddington, 

 and therefore beyond the limits of the Map. It is chiefly the lower part of the series of strata com- 

 posing the coal-field, which exists so far to the east. The limestone that is worked or known there, cer- 

 tainly belongs to the lowest part, and the thin coal-seams which occur in Haddington, at Amisfield, 

 Coalston, Morham, and other places mentioned in the Memoir, are also lower members of the basin. 

 This extension of the coal-field reaches to the sea-coast between Dunbar and Dunglass. 



It will be seen, that the part of the district occupied by carboniferous strata, — that is to say by 

 strata alternating with coal-seams and shales (which I look upon as constituting the coal-field proper,) is 

 coloured on the Map with a shade of indigo. 



The Old Red Sandstone formation — consisting of red Clays, Sandstones, and Conglomerates, is indi- 

 cated by a red colour. It must not, however, be supposed, that this formation exists only at the spots 

 indicated on the Map. These are the places, where I have ascertained its existence, — and I was un- 

 willing to extend the colour to other places which I had not examined, however strongly I might con- 

 jecture that the formation existed there. As the object of the Memoir was chiefly to describe the coal- 

 field, and the manner in which its members — aqueous and igneous — were disposed, it seemed of less 

 consequence to be very precise as to the older formations, and that little more was necessary in illustra- 

 tion of this Memoir than to indicate their existence and situation. 



It will be seen from the Map, that the greywacke rocks, both in the Lammermuir and in the Pent- 

 land hills, have received the same colour as that which represents the felspathic rocks. If the description 

 of these several rocks had formed any part of my Memoir, it would have beeu of course necessary, 

 though difficult, to distinguish them by separate colours. But as my object in representing at all on the 

 Map, any portion of the Lammermuir and Pentland range, was simply to point out the boundaries of 

 the coal-field, and the position of the rocks, which, by their degradation, had afforded, in some degree 

 at least, materials for some of its sedimentary strata, and which moreover had, in the opinions of some 

 geologists, been the means of elevating and dislocating them, — I considered it might be useful to indicate 

 the range of those hills, and the line of their nearest approximation to the coal-field. These objects 

 were sufficiently attained by using one colour to represent the hills, coupled with an intimation, that 

 it was by no means thereby intended to represent them as homogeneous, but as consisting of grey- 

 wacke and of felspar in various states. In one point of view, there is even a propriety for using one 

 and the same colour to represent these different rocks, — not merely because they form together one and 

 the same range of hills, but because they have, in my opinion, been raised at one and the same period. 

 I consider that the greywacke strata were burst through and elevated by great eruptions of felspathic 

 rocks. These eruptions must have taken place, probably about the same period, and apparently along 

 certain lines which run in a direction nearly east and west, — in many parts of the south of Scotland. 

 At most places, they brought up with them the deep-seated strata of the greywacke and Silurian epochs. 

 VOL. XIV. PART I. Y y 



