MR MILNE ON THE GEOLOGY OF ROXBURGHSHIRE. 



cipal joints run about north-east, the others about north-west. In the coal-seams 

 at Rowanburn (as Mr Gibson the manager informed me), the principal joints (or 

 backs as the colliers term them) run about due north, and the others due west. 

 Mr Gibson states, that these backs and cutters are independent of several large 

 faults which intersect the coal-seams, and which appear to be of subsequent 

 origin. He thinks also, that these joints are all independent of the dip and rise of 

 the coal-seams. 



In the greywacke, I have observed joints at only a few places. At Carolside 

 Bridge, there are numerous parallel joints intersecting the flesh-coloured greywacke 

 strata, in a north-north-west direction ; and a similar system of joints prevails in 

 the light blue strata at Clackmae. At Langholm Bridge, there are numerous joints 

 traversing obliquely the greywacke strata in a west-north-west direction, and 

 mostly filled with spar, which occasionally contains lead. 



There is thus a remarkable uniformity in the direction of the structural joints 

 of the stratified rocks, a direction apparently quite independent of their dip, 

 and formed at a date subsequent to their deposition. 



I may here also take notice of a vein on the south bank of the Tweed, op- 

 posite to Birgham, intersecting horizontal strata of clay and marl, and varying in 

 its width according to the nature of the strata passed through. In those marly 

 strata which contain a good deal of lime, the vein is from 2 to 3 inches wide, 

 and consists of crystallized carbonate of lime. In the other beds of dark red or 

 brown clay, which have no appearance of lime in them, the vein becomes a mere 

 crack of about ^ inch in width, and has no mineral contents. 



III. Lastly, I have to notice the Post-tertiary and Diluvial Phenomena, in so 

 far as at all remarkable in Roxburghshire. 



(1.) The oldest of the post-tertiary deposits is what has been termed Boulder 

 clay, because characterised by containing, interspersed through it, large boulders 

 or rounded blocks of stone. This deposit may be seen on the banks of the Leader 

 at different places, and also near Sprouston. It does not appear to exist in the 

 higher parts of the county. 



At Sprouston freestone quarry, there is a good section, shewing a bed of 

 boulder-clay from 2 to 8 feet thick, lying upon the sandstone, then a bed of fine 

 clay or silt free from pebbles, from 1 to 2 feet thick, lying over the boulder-clay, 

 and, lastly, a bed of small gravel, from 4 to 5 feet thick, immediately under the 

 soil. The boulders are all rounded, and consist of greywacke, porphyry, and 

 basalt. 



In regard to the existence of boulders on the surface, there are not many 

 places where they are in any abundance ; though it is more than probable, that, 

 before agricultural improvements commenced, the whole county had been covered 

 with them. 



VOL. xv. PART in. 6 i 



