MR MILNE ON THE GEOLOGY OF ROXBURGHSHIRE. 455 



The amygdaloidal tufa of Holm House, which is about a mile to the south- 

 east of the Eildons, appears to be much the same sort of rock as the tufa just 

 described. The Holm tufa presents a wall or face, which runs north-west and 

 south-east, and seems to run across the Tweed, forming a rapid. It effervesces 

 slightly with acids. Where most compact, this rock contains white and yellow 

 crystals of felspar. It contains also angular fragments of clinkstone and ancient 

 porphyry, and probably greywacke. This tufa may be traced for a considerable 

 distance up the burn which here flows into the Tweed. On examining the yellow 

 sandstone rocks, which are close to it on the south side of it, there are appearances, 

 in the structure of them, which indicate that they have been acted on by heat. 



At Moorhouselaw, about 2 miles south-east of Maxton, there is a sheet of 

 amygdaloidal porphyry, which has flowed over and among the red sandstones. 

 There is, in this porphyry, great abundance of chlorite and other minerals, formed 

 probably by chemical precipitation. 



3. The Augitic and Hornblende Rocks are next to be described. 



(1.) Among the oldest of this class, must be placed the well-known hills called 

 Ruberslaw, Bonchester, Bunion, and Peniel. The rock at Ruberslaw is greenstone, 

 containing steatite. That on Bonchester is basalt, containing crystals of augite. 



Around the hills just named, the red rocks prevail, and, up to within a short 

 distance of their summits, remain on all sides pretty nearly horizontal. At 

 Peniel Heugh, they are to be seen within 50 feet of the summit. 



There is a range of greenstone and basaltic rocks between the Fly Bridge 

 and Smailholm, which are to a considerable extent covered by the red rocks also 

 here horizontal. They bear the name of Black-craigs and Black-dykes, derived 

 probably from the dark colour of the basalt. The farm-steading of Sandyknow 

 is built on horizontal strata of red sandstone, and within 20 yards of the green- 

 stone rock, which seems to have in no respect affected the sandstone. These trap 

 rocks appear to continue eastward by Nenthorn to Stitchell and Hume Craigs in 

 Berwickshire. At Stitchell the basalt occasionally exhibits red stains, whether 

 caused by iron or red felspar I do not know. It contains also some beautiful 

 crystals of black glassy hornblende ; also of several other minerals, which are 

 unknown to me. One of these specimens I shewed lately to my friend Mr 

 JAMESON TORRIE, who states that it contains a morsel of mineral pitch, having 

 opal imbedded in it. 



To the west of Peniel Heugh, there are several protuberances of basaltic and 

 greenstone porphyries, which form with it a connected range. There is a patch 

 on the east side of the turnpike-road near Ancrum North Lodge. Another mass 

 occurs a little to the west of Ancrum House, at the Castle Hill, and at Scaw. 

 The stratified rocks are seen at the place last mentioned, within a few feet of the 

 trap, without being at all affected by it. To the west of Kirklands House, green- 

 stone again occurs ; as also about 2 or 3 miles farther west. 



