276 



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



figure illustrates this description. A is a covering of gravel and boulders. B are 

 the stratified deposits of disintegrated trap. C is the solid trap- rock on which 

 these strata rest. 



^Q.^-:----Y-<=i'-^: 



(2.) There are three or four dykes of trap in the district, all of them except one 

 consisting of greenstone. The dykes are all situated within the limits of the coal- 

 field proper ; at least they traverse and intersect for the greatest part of their coiirse 

 the workable coal and lime strata; and if they run out beyond the limits, it is merely 

 to join the hUls of trap, which are on the immediate confines of the coal-field. 

 The first of these dykes which I may refer to, runs in an east and west direction, 

 about a mile south of Portobello. The line of it is crossed once or twice by the 

 Brunstain Burn. It runs in a direction N. 60° W., and its course is indicated on 

 the map by a double line, coloured green. It consists chiefly of clay, but containing 

 also a good deal of felspar ; and it contains other minerals common to trap -rocks 

 of that description. Its texture is tough, and it has a greenish-brown coloiu-. In 

 one place not far from the new road leading from Dalkeith to Leith, it was formerly 

 quarried for the roads. It is there 50 or 60 feet wide. But it gets gradually thinner 

 towards the east, and terminates near Brunstain-house. It has not been traced 

 ferther M'est, I believe, than Niddry Mill, so that its known and ascertained course 

 is not more than one and a half miles in length. It is extremely probable that 

 it is connected with Arthur's Seat, the trap of which is in one part of the hill si- 

 milar to it in texture. 



Another dyke may be traced from Morison's-haven by Preston, Seaton, Red- 

 coll, and so eastwards towards the Garlton hills, a distance of nine or ten miles. 

 This dyke varies greatly in thickness. At Morison's-haven it appears to be some 

 hundred feet thick ; at Bankton (about three and a quarter miles east from this 

 point) it is about 00 feet ; at Mr Cadkll's railway (where it is quarried for the 

 roads) the north side or " veeze" of it is visible, but not the south side ; — what is 

 visible measures 96 feet. Near Long Niddry, where it has been also quarried, 

 this dyke appears to be not more than 50 feet wide. This dyke runs in a direc- 

 tion E. by S. 



It wiU be observed that, on the map accompanying this, the Morison's-haven 

 dyke is represented as inteiTupted near RedcoU. I do not know whether it there 

 takes a turn to the south, — an occurrence to which I know no analogous case, — 

 or whether there is another dyke which runs from that point towards the Garl- 

 ton hills, along a parallel Une, which is situated half a mile to the south of the 

 line of the Morison's-haven dyke. Certain it is, that a greenstone dyke, though 



