202 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



dhui and Cairn Gorum Mountains. So little does it appear to have 

 been affected by these great igneous masses, that I have been al- 

 most disposed to believe that it may have been deposited on the 

 granite at a period subsequent to its consolidation. Be this as it 

 may, there is no doubt that this great formation of gneiss, lime- 

 stone, and quartzite rests on the mica-slate of the southern Gram- 

 pians, and is thus a newer formation. I have also no doubt that it 

 is a continuous portion of the same great gneiss and quartzite forma- 

 tion which we have seen in the Breadalbane Highlands overlies the 

 mica- slate of Loch Tay and Glen Dochart. 



19. Clay -slate of Loch Creran. — I shall not at present follow this 

 series of deposits north into Aberdeenshire and Banffshire, but turn 

 now to its relation to the slate-rocks of the south-west. These are 

 by no means so clearly seen as might be wished, probably in conse- 

 quence of the great eruptions of igneous rocks of diverse kinds and 

 of very different ages. In the south-west it abuts against the 

 granitic mass of Ben Cruachan. Near Dalmally and Loch Awe, this 

 mountain is skirted by schistose rocks, but these I regard as belonging 

 to the mica-slate formation more probably than to the gneiss. Beyond 

 this granite mountain-group, in the angle between Loch Creran and 

 Loch Leven, there is a great development of schistose beds, classed 

 partly as clay-slate, partly as mica-slate. A fine section of these 

 beds is exposed near Appin and along the shores of Loch Creran. 

 At Port Appin quartzite appears on the shore and extends north- 

 east along the Limine Loch. Generally it is composed of distinct 

 grains of quartz in a finer quartz basis, with a few crystals of iron- 

 pyrites or felspar, the latter well marked by weathering to an opaque, 

 white colour. In some places, however, the quartzite is a mere 

 mass of quartz-veins with no marks of stratification, and in many 

 cases may almost be regarded as a binary granite composed of abun- 

 dant quartz with a little felspar. Where most distinctly stratified it 

 dips 60° or 70° to W. 20° S., and thus runs in a direction N. 20° W. 

 Proceeding east towards Loch Creran, mica-slate, often talcose, begins, 

 and forms the great mass of the country with very little diversity of 

 character. It first dips E. 35° to 40° S., but, about two miles east 

 from Appin, forms a synclinal, beyond which the dip is very predo- 

 minantly W. 30° ET. at angles ranging from 45° to 60°. The beds 

 are strongly undulated, and in many places show a transverse cleavage 

 or grain. This peculiar character is beautifully seen on the weathered 

 surface of the rock near Creigan Ferry, where it approaches in mineral 



aracter to gneiss. The two sets of planes dip nearly in opposite 

 directions, — the one at 55° towards N". 52° W., the other 43° towards 

 S. 52° E. ; and in another place, the first at 56° towards N. 64° W., 

 the second at 20° towards S. 64° E. The first is probably the true 

 dip, as it is the more continuous, and also as it is parallel to the 

 change in the mineral character of the beds. Great veins of quartz 

 also run along these divisions or bedding. In either case the mica- 

 slate in this locality is unconformable to the quartzite, as clearly 

 shown by the direction of the beds. This is — 



