1849.] NICOL ON THE SOUTH-EAST OF SCOTLAND. 61 



When we contrast the decided unconformity that always appears 

 in Scotland between the Silurian strata and the formations that rest 

 on them, with the perfect parallelism which has been shown to exist *, 

 in the typical region, between deposits of the same age and the over- 

 lying old red and carboniferous rocks, the argument becomes still 

 stronger. With such proofs that these ancient disturbances are merely 

 local, and have not affected all the rocks of one age even in the same 

 country or limited district, we can hardly be expected to believe that 

 their influence has extended over the whole of Europe, and even into 

 the more distant regions of Asia and America. 



The dip of the strata in this range of mountains is far less regular, 

 either in amount or direction, than their line of strike. On laying 

 down, however, my observations on the map, it appears that towards 

 the northern margin of the Silurian rocks, the dip is generally north- 

 wards, whereas as we proceed south a change takes place, and the dip 

 is more frequently to the south. Though there are numerous ex- 

 ceptions, still this fact indicates the occurrence in this part of the chain 

 of an anticlinal axis over which the beds have been folded. Taken 

 generally, this axis will pass from the group of felspar porphyry hills 

 east of Inverleithen to Loch Skene north of Moffat, where igneous 

 rocks also abound. It thus runs along some of the highest mountains 

 south of the Forth ; and the mineral springs at the localities j ast named 

 are probably connected with this line of ancient igneous action. Its 

 general direction is considerably more to the north of east than the 

 average deduced for the strata. 



The position of this axis of elevation so near the northern boundary 

 of the Silurian rocks is a point of much interest, from its apparent 

 connexion with some of the most remarkable physical peculiarities of 

 the country. On examining a geological map of Scotland it will be 

 seen that the boundary between the red sandstone and the Silurian 

 formations on the south is very irregular, the newer deposits forming 

 many indentations in the older. It was thence inferred that the red 

 sandstone had been deposited in valleys eroded in the greywacke rocks 

 at a very early periodf . The northern margin presents a different 

 outline. The border there is for great distances nearly a straight line, 

 with few sinuosities. Thus from the trap hills at the sources of the 

 Nith, the line of junction runs almost direct to Howgate near Penny- 

 cuik, where it bends slightly to the south, but soon resumes a recti- 

 linear direction towards the north-east to the coast at Dunglass, where 

 it again curves round to the south. Along this line, especially to- 

 wards the east, the junction of the two formations is marked by a 

 range of hills composed of highly inclined Silurian strata, against 

 which the red sandstone and carboniferous rocks abut m nearly hori- 

 zontal beds. In some places this appearance is concealed by the 

 igneous formations, especially those connected with Tinto and the 

 Pentlands, but to the south of Edinburgh and along the base of the 

 Lammermuirs it is very distinctly marked. In many ^places the close 



* See Murchison's Silurian System, chap^xlii. p. 568, &c., where the incon- 

 sistency of this fact with the theory of M. E. de Beaumont is very clearly ex- 

 plained, t Journ. of Geol. Soc. vol. iv. p. 200. 



