182 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



3. Clay-slate Formation of Bute. — The first formation I shall 

 notice is the clay-slate. This, as shown by Dr. Macculloch and in 

 my own map, forms a narrow band along the southern flank of the 

 Grampians, from Arran to Stonehaven, everywhere presenting very 

 similar and unmistakeable characters. These it is unnecessary to 

 repeat, and some local peculiarities will be noted in the special sec- 

 tions. I shall also pass over its relations in Arran, only remarking, 

 that the granite appears to have risen up nearly in the line of junc- 

 tion between the clay-slate and the mica-slate. In Bute the clay- 

 slate dips to the S.E. at angles ranging from 20° to 60°, and appears 

 to rest on the mica-slate, also dipping in the same direction. Some 

 sections near Rothsay have led me to suspect that in this island 

 there are two formations of the clay-slate, as intimated by Mr. D. 

 Sharpe, the upper green or light-grey slates appearing to rest un- 

 conformably on the lower blue slates. 



4. Loch Long and Gareloch. — On the mainland a similar S.E. dip 

 prevails along the Eirth of Clyde, though in some plaees, as near 

 Dunoon, the outer range of clay- si ate can scarcely be said to occur. 

 On the Gareloch a better section of the clay-slate in its relation to 

 the mica-slate is seen, though still in some places concealed by de- 

 tritus. This section is represented in fig. 1, beginning on the north 



Eig. 1. — Section on Gareloch. 



N.W. S.E. 



Loch Gareloch Rose- Firth of 



Long. Head. neath. Clyde. 



Mica-slate. Clay-slate. 



side of Loch Long, near Castle Carrick, and extending to the Clyde, 

 near Roseneath. 



On the north side of Loch Long the mica-slate, rising up into the 

 gnarled and rugged mountain -group known as Argyll's Bowling 

 Green, forms an anticlinal axis, apparently oblique to the direction 

 of the loch. On both sides of Loch Long the mica-slate is so twisted 

 and contorted that the dip is almost undeterminable. Occasionally 

 the beds are horizontal, then they dip to the north or south at angles 

 ranging from 15° to 80°, or, again, are, as it were, twisted in both 

 directions in the most complex manner. The average direction is, 

 however, N.E. by E. (or N. 55° E.), and thus nearly parallel to the 

 general range of the strata. Several dykes or veins of greenstone 

 intersect the strata, but do not produce much change either on their 

 direction or character,. 



The strata, generally a distinct lustrous mica-slate, intersected by 

 quartz-veins, continue to dip S. 35° E. from Loch Long to Gareloch 

 Head. Near the latter place the beds become more regular, with 

 an average dip of 70°. Further down the Gareloch the rocks are 



