134 Reports and Proceedings. 



Edinbtjegh GtBOlogical Society. — At the second ordinary meet- 

 ing of the Society for the present Session, held on 2nd December, 

 1869, A. Geikie, Esq,, F.E.S., etc., President, in the chair, the first 

 paper was "On the Succession of the Laurentian, Cambrian, and 

 Lower Silurian Rocks on the Shores of Loch Broom, " by Sir 

 Eoderick I. Murchison, Bart., K.C.B., etc., being a letter addressed 

 to the President. . . ... " The few additions which I made last 



summer to my acquaintance with the Highland rocks were in the 

 west of Eossshire, and particularly on the shores of Loch Broom, a 

 district which I rapidly traversed with Professor Sedgwick in 1828, 

 and to a part of this very Ullapool you extended the researches we 

 were making together in 1860. What I have to state is the result 

 of a visit to my friend, Mr. John Fowler, the eminent engineer, and 

 proprietor of a large extent of Highland country at the western end 

 of Loch Broom, who has erected a noble mansion called Braemore, 

 which, being nearly 700 feet above the sea, commands an extensive 

 view over Loch Broom up to the mountain of Ben More. Possess- 

 ing a small steam-yacht, he enabled me to make excursions to points 

 which I had before only seen very imperfectly. In this tract — i.e., 

 from the numerous low Summer Isles which crowd the outermost or 

 western portion of the sound — the Priest and others of them are 

 composed chiefly of the Fundamental Gneiss, which in 1859 I 

 paralleled with the Laurentian rocks of North America. Also, on 

 one of the promontories of the southern mainland, called Cailleach, 

 this Laurentian gneiss is seen to throw off, on its broken edges, 

 patches of the coarse reddish brown grit and conglomerate which 

 constitute the southern shore of Loch Broom ; the Cambrian grits 

 being thrown off at various steep angles. On the northern side of 

 the loch, however, the same Cambrian rocks constitute the whole of 

 the lofty mountain of Ben More, the strata of which are clearly 

 seen from the water to constitute a succession of terraces very 

 slightly inclined to the east, and thus exhibiting a thickness of 

 several thousand feet. Some of the lowest portions of these Cam- 

 brian rocks consist of hard schists. As a whole these rocks are 

 precisely similar to those of the same age which I had formerly 

 described in Sutherland. Their lithological characters are also 

 similar. Thus, the Laurentian gneiss at the point of Cailleach is like 

 that of Loch Inver, essentially a hornblendic, rough, thick-bedded 

 gneiss of highly crystalline aspect, and more or less dull greenish 

 colour, occasionally quite finely laminated, and showing, by the 

 arrangement of the quartz and felspar within it, a bedded character, 

 -with small crystals of garnets occasionally disseminated. At this 

 locality it only differs from the bottom rocks of Sutherland and the 

 Lewis in being less granitic, and with fewer interpolations of pure 

 granite. The Cambrian rocks which overlie transversely that 

 Laurentian gneiss are essentially, as in Western Sutherland, coarse 

 grits, in parts conglomeratic, and made up of the materials of the 

 older gneiss — i.e., of quartz, hornblende, and felspar — but, like the 

 parent rock from which they have been derived, they contain little 

 or no mica. These sandstones and grits, for -the most part of a 



