MR MILNE ON THE GEOLOGY OF ROXBURGHSHIRE. 451 



taining imbedded portions of grey wacke, a fact of itself sufficient to shew, that 

 these hills were thrown up after the greywacke strata were deposited. 



These hills are remarkable for the columnar ribs of flesh-coloured felspar which 

 occur on their south-west side, opposite to Bowsden. Some of them exceed 30 

 feet in length. I do not know any other place in Great Britain, where this species 

 of trap exists in the form of such gigantic crystallization. 



Bemerside Hill, which consists of a yellow or buff- coloured felspar, belongs 

 apparently to the same epoch. In this rock, where quarried on the south side of 

 the hill, I observed conchoidal fractures on a very large scale. Some of them 

 form elliptic figures fuUy 15 feet in diameter. It may be supposed that in igneous 

 rocks, such an arrangement of matter as these conchoidal surfaces indicate, may 

 be readily explained by the process of cooling. But similar appearances, and on 

 nearly as large a scale, are not uncommon in sedimentary rocks, producing what 

 the quarrymen call " yokes" or hard concretions. 



At Easter Softlaw and Frogden, the felspar assumes the form of a compact 

 fine-grained clinkstone, of a purple colour. This seems to be about the northern 

 limit of the old felspathic rocks of Cheviot. 



At Windburgh, the rock is clinkstone, and of a still darker hue. The old red 

 sandstone can, at several places on the east side of this hill, be seen within a few 

 feet of the igneous rock, and perfectly horizontal. 



On the west and south-west sides of Minto Crag, which is clinkstone of a dark 

 colour, there is a yellow slaty sandstone within 10 yards of it, quite unaffected. 



In Ancrum Park (Sir W. Scott's), a bed of claystone porphyry (containing 

 large crystals of felspar) may be seen in a burn below the dog-kennel, overlaid by 

 slaty horizontal strata, which appear to consist partly of felspar, derived probably 

 from the decomposition of the subjacent beds. Over these the red sandstones are 

 lying undisturbed and unaltered. 



(2.) In regard to felspar rocks of a later date, I would, in the first place, refer 

 to an elevated mass or sheet of felspar porphyry, stretching across the Teviot and 

 the Tweed from the south by Springwood Park to Mackerston. The texture of 

 the rock is there coarse and friable, and not nearly so crystalline as the trap-rocks 

 last described. There is, however, a vein in it (to be seen in the channel of the 

 Teviot above Springwood Park summer-house) much more hard and fine-grained. 

 This vein is in one part red, and in another grey, in its colour. It is visible for 

 about 20 feet, running by compass west 4 north. It is from 6 to 8 inches wide. 



This flow of felspar porphyry has produced remarkable effects on the strata 

 adjoining it, both in the Teviot and in the Tweed. The coal sandstones have evi- 

 dently been made to undergo great changes in their internal structure. Near the 

 porphyry they are highly crystalline, and the calcareous matter has separated 

 from the siliceous, in a way altogether unusual in this rock, except in such situa- 

 tions. The trap appears to have flowed among and between the stratified rocks, 

 and thus partakes of their dip, as may be well seen near Roxburgh and Sprouston. 



