FROM THE NORTH-WEST HIGHLANDS. 421 



that the section exhibited by the author appeared correct in its 

 general principles, the quartzo-dolomites formiDg a sort of veneer 

 on the front and summit of the mountain. As regards the Dalbeg 

 marbles, these were very singular rocks, mixtures of granular calcite 

 with a pyroxene (?) mineral, whose magnesia was partly in a state 

 of serpentine. He should like to know the relations of the author's 

 Caledonian series with the Hebridean. Dr. Callaway's results cor- 

 roborated in the main the stratigraphical views of the late Prof. 

 Nicol as to much of the Assynt country. Mcol was understood to 

 have admitted that some of his work in the north-west might not 

 be strictly accurate; but he predicted that the ultimate explanation 

 would take all by surprise. 



Mr. Topley asked if Professor Bonney would give his opinion as 

 to the nature of the Logan Rock and of the Dalbeg marble. 



Prof. Bonney said that he had only seen the so-called Logan Rock 

 in one locality in the field, viz. in Glen Logan, near Loch Maree. 

 There in some parts it no doubt had a considerable resemblance to 

 a coarsely crystalline igneous rock ; still both macroscopically and 

 microscopically it corresponded better with a granitoid metamor- 

 phic rock. In some parts it was certainly a gneiss ; almost every- 

 where it bore marks of great crushing. Some of the dark schists 

 (probably the serpentinous rocks of some authors) proved to be 

 nothing but the Hebridean gneiss crushed near faults. It was cer- 

 tainly not an intrusive rock in Glen Logan. The specimens which 

 he had received from other regions, sent to him by Dr. Hicks, 

 Dr. Callaway, and others, were similar in their nature, Hebridean 

 gneissic rock more or less crushed. If there was igneous rock in the 

 " Logan Rock " it was only local. As regarded the Dalbeg marble, he 

 had not worked much upon it, because he knew that Dr. Heddle 

 had been for some time engaged in studying it. He would merely 

 say that it consisted of crystalline calcite (with, perhaps, dolomite) 

 and a whitish pyroxene (malacolite) partially replaced by a serpen- 

 tinous mineral. Here and there it showed a structure very like 

 Eozoon. He thought from the general appearance of this rock that 

 it would be found to be distinctly of Archaean age. 



Prof. Lapworth said that he had for some years been of opinion 

 that in the Highlands we must expect to find the same phenomena 

 as in the great mountain-ranges on the continent. He had con- 

 sequently listened with great pleasure to the paper, the more so as 

 he was personally ignorant of the Assynt district ; but Dr. Calla- 

 way's interpretation of the structure of that area coincided with 

 what he had himself worked out in the Erriboll district. Here, 

 however, the difficulties were far less than appeared to be the case 

 in the Assynt district. He then pointed to some sections and a map 

 of the Erriboll area, which he had brought with him, showing the 

 Erriboll limestone generally occupying the centre of a synclinal 

 fold, and underlain by a series of flags and quartzites identical with 

 those recognized by Dr. Callaway in Assynt, and repeated again and 

 again in refiexed folds. There was generally a great overfold and 

 fault, which threw the Sutherland series irregularly onto the quart- 

 er J. G.S. No. 155 2h 



