W. H. Hudkston — First Impressions of Assy nt. 397 



alwaji'S struck me as subsisting between the two, tbongb I am far 

 from saying that they are absohitely identical. 



What then is the function of this " Logan " rock throughout the 

 eastern range of Assynt from the precipitous shores of Loch Glen 

 Coul to the termination of the range near Loch Borrolan ? Is it not 

 in reality the framework or core round which the newer formations 

 are folded, sometimes in great winding sheets of white quartzite like 

 those in which Breabag is swathed ? Not that these were ever 

 deposited upon their base, whatever it may have been, in its present 

 position. That base has been elevated to the heights it now occu- 

 pies in the crush which has produced these convolutions and dis- 

 locations. The general result of these movements seems to have 

 been the establishment of an irregular synclinal in the longitudinal 

 hollow between the west and east ranges, so that the gently sloping 

 Quartzite of the one reappears in all sorts of positions round about 

 the sides and summits of the other, with fragments of the Dolomite 

 occurring in the most unexpected places and in every attitude. In 

 such a hill as Breabag the framework does not show through the 

 clothing, the Quartzite is unbroken, and wonderful has been tlie 

 plasticity of the rock which could endure without fracture such 

 foldings as may be seen in the Bealloch between that mountain and 

 Coniveall. It is probable also that the thickness of the Quartzite 

 itself varies materially within short distances. 



The explanation of a core of gneiss very well suits the appearances 

 on both the north and south sides of the ridge connecting Coniveall 

 with Ben More. It will be remembered that on the north side 

 " Logan " rock continues beneath this ridge to a height of about 

 2500 feet, before the grits and conglomerates succeed, which lie at 

 the base of the presumed Upper Quartzite on this mountain, but 

 nowhere else as far as I can make out. The same phenomenon may 

 be noticed on the south side in the wild corries round Dhu Loch 

 More. " Granitic gneiss, and mica slate with intrusive rocks," says 

 Nicol,^ "constitute the nucleus of the mountain." His granitic gneiss 

 and mica-slate are, I apprehend, nothing more nor less than our 

 "Logan" rock, which extends to an elevation of about 2550 feet 

 (by aneroid) on the S.E. shoulder of Coniveall. At this point the 

 usual granitic and hornblendic assortment of crystalline rocks, 

 varied by a little porphyry in places, suddenly terminates, and is 

 succeeded by the coarse fragmental series underlying the Quartzite. 

 These beds dip 25° W.N.W., i.e. rather into the mountain, which may- 

 receive strength from a slight local syncline. Thus on both sides 

 an elevation of at least 2500 feet must be claimed for the " Logan " 

 rock of the Ben More-Coniveall group, leaving about 700 feet for 

 grit beds, conglomerates, quartzites and the like. 



It was the sight of this magnificent corrie at the head of Dhu Loch 

 More, with the entire sweep of its precipitous slopes, thus obviously 

 composed of " Logan " rock, with a mere capping of Quartzite, which 

 at once staggered my faith in the Murchisonian interpretation of 



1 Q.J.G.S. vol. cit. p. 99. 



