﻿160 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 5, 



consisting of flaggy, grey-coloured, and purple, hard greywacke with 

 occasional courses of black schists. 



At Rae Cleugh, near the turnpike-gate, any one looking at the 

 form of the adjacent hills on the east would suppose that the sharp 

 slope on the north was an escarpment, and that the strata would 

 really be found to dip in the direction of the southern gentle slope. 

 The actual section, however, of the railroad shows the very reverse, 

 and exhibits the strata plunging N.N.W. at angles varying from 40° 

 to 50°. Professor Sedgwick, who had previously examined this tract 

 and collected many Graptolites from it, invited me indeed to try to 

 mark the real axis of this central country by attending to the talus and 

 scarp, or short and long slopes of these mountains. But however well 

 I found this outline explained the folds of the strata in the Alps*, 

 the test was worth nothing in this the highest tract of the South of 

 Scotland. 



In advancing to the summit-level of the railroad, wherever a dip 

 is exposed it is still to the north ; but, as considerable spaces are ob- 

 scured and denuded, and no cuttings are visible, it is probable that 

 there may be rapid flexures and fractures which cannot be detected 

 in this rounded, grassy country. At the last cuttings near the 

 summit-level, purple greywacke is followed by hard glossy schists with 

 quartz veins, crystals of iron pyrites, &c, the whole dipping 75° to 

 the N. or N.N.W. The descent of the railroad exposes only two 

 cuttings, the valley being level and thickly covered with drift ; but 

 these also exhibit a northerly dip, and, from all that is visible, the 

 same inclination is really continued to Abington ! Professor Nicol, 

 who examined the country near that place whilst I turned to the south 

 to look at the strata near Lockerby, could detect there no trace of true 

 limestone, but he found a light-grey, flinty slate, unlike any rock we 

 had previously seen, and evidently, as he thought, metamorphic. 

 Among those beds was a rude breccia of prismatic clay-slate mixed 

 with limestone ; the fragments of the latter having much the colour 

 and aspect of the Wrae limestone in Peebleshire, which, according to 

 the general strike, is in the direction to which this breccia would ex- 

 tend. It is therefore probable that the breccia is a thin continuation 

 of the Wrae limestone, broken up and altered by the red felspar-por- 

 phyries and other igneous rocks which abound in this district. This 

 is the tract of all others in the South of Scotland where the grey- 

 wacke and clay-slate have been most modified, as around the base 

 of the porphyry of Tinto Hill and in the Lead Hills. It has afforded 

 the greatest amount of metalliferous veins, and in ancient times it 

 was the site of gold-works amidst the drift derived from the altered 

 rocks. We cannot look for order in such a tract. If, indeed, the cal- 

 . careous breccia above alluded to be really the equivalent of the Wrae 

 limestone, it seems rational to infer that the masses of schist, rising 

 out from beneath it to form the highest hills of the region, are, as 

 Professor Nicol suggested in 1849f, and revived in a discussion at 



'* See Quart. Journ. Geol. Soc. vol. v. p. 239 et seq. 

 f Ibid. vol. vi. p. 61. 



