452 MR MILNE ON THE GEOLOGY OF ROXBURGHSHIRE. 



In the Tweed, about 1^ mile below Mackerston House, on the north bank, 

 the marls and sandstones of the coal formation are hardened in a somewhat simi- 

 lar, though not in so striking a manner. 



These sheets of porphyry have in all probability flowed down from the Che- 

 viots, but at a period subsequent to the elevation of the Cheviot proper. Accord- 

 ingly it is found, though in a less friable state, at Hightown, about a mile to the 

 south of the Teviot. In a quarry of it south of this village, I noticed a vein of com- 

 pact red felspar running north-west, cutting through the more shivery rock. I 

 picked out a quantity of earthy copper-ore from the sides of this vein. 



The felspar porphyry (already described) at Sprouston, Kerchester, Hadden, 

 and Carham, lower down the Tweed, belongs evidently to the same epoch, and has 

 produced effects precisely similar on the strata of sandstone and marl which oc- 

 cur there on both banks of the Tweed. At Hadden, near Sprouston, and at 

 Sucklawrig, near Mackerston, the trap has a green earthy basis, having numerous 

 plates of brown mica disseminated through it. 



It rather appears to me, though I am by no means confident, that the Black 

 Hill of Earlston, sometimes called Cowdenknows Hill,* also belongs to this later 

 epoch. It is a felspar porphyry, the colour of the rock being, like that of the Eildons, 

 brick red. The red rocks reach to within about 200 feet of the top of this hill, and 

 dip from it at a considerable angle. 



There is a small patch of felspar precisely similar to that composing Cowden- 

 knows Hill, on the west side of the Leader, near Clack-mae, as shown on the 

 map ; and there are some remarkable dykes, also of the same rock, which, in va- 

 rious parts of the county, may be seen traversing the old red sandstone strata. 

 I shall mention some of the places where I have observed these. 



Just below Chappie (on the Leader), a felspar-dyke of a greyish-red colour, 

 and about 18 inches wide, cuts through the old red sandstone conglomerate, in a 

 direction east by south and west by north. It corresponds exactly with the strike 

 of the grey wacke strata at this place. 



Below Carrolside (also on the Leader) the edges of the greywacke strata 

 stand up about 6 feet above the channel of the river, and are covered by the con- 

 glomerate of the old red sandstone, which here forms a bank not less than 200 

 feet high. At this place a dyke precisely similar in texture and colour to the one 

 above noticed, and about 6 feet wide, is seen shooting up from between the 

 greywacke strata, and piercing the conglomerate. The greywacke strata here 

 are very nearly vertical, and run east by north. The dyke runs in the same di- 

 rection. The following section is meant to illustrate this interesting meeting of 

 rocks. 



* On the top of this hill are the remains of a vitrified fort, consisting of two ramparts. The rock 

 was well adapted for being fused, from the quantity of alkali it contains, a quality of which the manu- 

 facturers of these forts seem to have been well aware, as the stones in all vitrified forts are of this 

 description. *- 



