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



275 



It is of course unnecessary for me to say one word of the trap-rocks at 

 Lochend, Calton Hill, Arthur's Seat, Braid Hills, or the Pentlands. They are too 

 weU known to need any description here. Let me allude, however, to the Black- 

 rock-basalt, which I do not think has been before noticed. It occurs about half 

 a mile beyond the crop or outburst, as it is called, of the Crichton-dean limestone. 

 It is there extensively quarried for road metal. The popular name of blue whin- 

 stone gives a tolerably correct idea of its appearance. What struck me as most 

 interesting about this whinstone, is the form of its arrangement. It consists of 

 large cylindrical masses, though of irregiilar shape, some of them five or six feet 

 in diameter. These masses are associated together in the form of columns or 

 round pillars, about ten or twelve feet in diameter, and reaching to a depth that 

 has not yet been fathomed. The quarrymen work the rock by digging out of 

 these pillars the indi^ddual masses of whinstone ; and when they have been 

 worked to a considerable depth, these spots present the appearance of Avells — or 

 rather of niches, as they are cut open on one side. The quarry having been ex- 

 tensively worked, there were, when I visited the quarry, eight or ten of these 

 niches, which presented a singular appearance at a distance. These semicu-cular 

 hoUows are separated from each other by a few inches (not exceeding 18), the 

 interstices being filled up with disintegrated basalt and argUlaceous matter, which 

 form veins. The structure of this rock is no doubt owing to imperfect and ex- 

 tensive crystallization, somewhat similar to what may be seen at Arthur's Seat. 

 The following section may help to render more intelligible the description that 

 has now been given. AB is a section of the hiU. C, C, C" are the cavities out 

 of which the trap has been quarried. 



At the west end of the Garlton hills, there is a section presented in a quany 

 which is worthy of some notice. Over the solid rock are several strata of disin- 

 tegrated trap, consisting of lilac-coloured clays, and smaU grained conglomerate, 

 each of these strata being not more than a few feet in thickness. The whole sec- 

 tion is about 12 or 15 feet deep, and 20 or SO yards long. They slope at an angle 

 of 10° or 12° firom the Garlton hills. They are overlaid by the debris of gravel 

 and boulders which every where cover the strata of the district. The following 



