424 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 16, 



north and south direction, predominating on the west coast*. I also 

 referred the origin of the former line to the outburst of the older 

 granites ; of the latter rather to the newer porphyries and traps. 

 Subsequent observations have greatly confirmed these views, and im- 

 pressed me with the conviction that the most marked features in the 

 physical geography of Scotland may be referred to the great W.S.W. 

 and E.N.E. line of elevation on the one hand, and on the other to a 

 second great line of upheaval running nearly north and south along 

 the west coast, and passing as it were into the first line in the re- 

 markable fissure of the Great Glen. 



Though the crystalline strata on the southern margin of the High- 

 lands are thus identified with the clay-slates and greywackes of the 

 southern Silurian rocks, I would not extend this view to the great 

 gneiss formation (including much quartz rock) which covers about 

 one-third of the whole surface of Scotland. I have not yet had suf- 

 ficient opportunities of examining the relations of this rock to the gra- 

 nite and mica-slates with special reference to the question, to speak 

 with confidence on the matter. Be this as it may, it seems evident 

 that we need look for no lower group of fossiliferous strata below the 

 Silurian in this part of the kingdom. If these have been converted 

 into crystalline clay-slates and mica-slates, any lower group of rocks 

 must have been much more highly metamorphosed, and all trace of 

 organization — if such ever existed in them — wholly obliterated. 



The red sandstones and coal-measures show a connection on the 

 one hand with the rocks of the same age in the central district of 

 Scotland, and also with the small deposit of coal formerly wrought 

 near the Fair Head on the opposite coast of Ireland, which also rests 

 immediately on crystalline strata. We have here the western termi- 

 nation of the great gulf or basin in which the carboniferous strata of 

 Scotland were deposited. The outlines of the margin of this carbo- 

 niferous basin may thus be pretty accurately traced out on the west, 

 whilst on the eastern side it probably opened into the great sea on 

 whose shores or gulfs the coal of the north of England was deposited. 

 This definition of the margin of the carboniferous sea may so far 

 compensate for the erasure of the lias from this part of Scotland, 

 where it seemed to form a valuable connecting link between the 

 mesozoic Irish strata and those of the Hebrides. 



The changes now introduced into the geological map of Cantyre 

 show that its structure bears the closest analogy to that of the neigh- 

 bouring island of Arran. In both localities there is a nucleus or basis 

 of old crystalline strata, on or around which a deposit of red sand- 

 stone and coal has taken place, all of them again broken through, 

 altered, and overlaid by igneous rocks, — predominantly felspar and 

 claystone porphyries. Both districts have subsequently been invaded 

 by innumerable veins of augitic trap-rocks ; these veins are seldom 

 of great width, but often continuous in nearly straight lines for long 

 distances. In the lower red sandstones of both regions conglome- 

 rates also prevail. The absence of primary boulders in the conglo- 

 merates of Cantyre recalls the fact, noticed by Sir R. Murchison and 

 * Geology of Scotland, p. 11-16. 



