W. H. Rndkston — First Impressions of Assynt. 395 



requires an explanation necessitating reference to other localities. 

 It is in fact the "igneous" rock of Nicol and Murchison, which 

 plays such an important part in confusing the geological structure 

 of the country and the sequence of the beds ; so that it may be 

 looked upon as one of the prime authors of the controversy on the 

 North- West succession, and a most difficult nut to crack. This 

 kind of rock is well developed in Glen Laggan or Logan near 

 Loch Maree, where it is very accessible in the bed of the stream. 

 A few years ago I ventured to point out ^ some of the peculiarities 

 of this rock, and referred especially to the stiings of epidosite which 

 pervade it. From its association with other bedded masses, and 

 from its general appearance, I came to the conclusion that it was 

 " an old gneiss partly invaded by extravasated matter." In the 

 following year Professor Bonney visited the same district, and, 

 in describing this very rock, went a step farther and classed it 

 with the regular Hebridian gneiss. 



This "Logan" rock occupies a large surface in the Assynt 

 country, and more especially in the eastern range, of which Ben 

 More is the highest peak. A glance at Dr. Heddle's map of 

 Sutherland will at once show its importance in this area — an 

 importance which could hardly be gathered from an inspection 

 of Professor Geikie's general map of Scotland. But large as this 

 area is, it might be extended in the great corrie on the north 

 side of Ben More previously mentioned. Dr. Heddle controverts 

 the views that it can either be the older gneiss, or an eruptive 

 igneous rock : he regards it as conformably interbedded, its horizon 

 being chiefly between the Dolomite and the Upper Quartzite. 



1 confess that, with every wish to accept my kind friend and 

 cicerone's reading, I was unable to endorse this position, and would 

 much rather fall back upon a modification of Nicol's interpretation 

 of the district, as exhibited more especially in his section of Glasven.^ 

 This, if we omit an inch from the east end, is not an unfaithful re- 

 presentation of the appearances both about Loch Glen Coul and 

 Glasven, when certain modifications are made. The " syenite " of 

 Nicol, in this section, represents the position of the "Logan" rock, 

 and he is probably not so far wrong in representing the Quartzite 

 (which should however have a capping of " yellow beds " if not of 

 regular Dolomite) as merely abutting on the rounded knolls which 

 rise up behind. The true continuation of the broken-ofif ends must 

 then be sought in the so-called " Upper " Quartzite which prevails 

 at greater heights to the eastward. 



It would be far too long a story to go into details on this impor- 

 tant point, viz. the junctions of the Quartzite-dolomite with the 

 apparently overlying " Logan " rock. Dr. Heddle has discovered a 

 remarkable section in the most precipitous cliff on the south side of 

 Loch Glen Coul, about a mile or so from the head of the Loch, to 

 which section he conducted Dr. Callaway and myself. Here the 

 dolomitic series, considerably modified perhaps in its development, 



^ Gneiss Eocks of the North- West Highlands, Proc. Gaol. Assoc, vol. tI. p. 75. 



2 QJ.G.S. vol. xvii. p. 95. 



