398 W. H. Hudleston — First Impressions of Assy nt. 



Assynt. I admit that there are plenty of difficulties still, and that much 

 has to be explained which I had no time to see. These are but first 

 impressions ; yet I should be very loath to believe that, because a 

 few sections may seem to show some tortured and dislocated frag- 

 ments of the Quartzite-dolomite appearing to pass under " Logan " 

 rock, that this great and continuous mass is not really from top to 

 bottom the local representative either of the fundamental gneiss, or 

 of something that is first cousin to it. This is the conclusion which 

 seems to render a part at least of the sequence in Assynt intelligible, 

 though the notion of an intercalated "Logan" rock, which has not a 

 few supporters, may work better in other districts. 



3. Is the Upper Gneiss really a newer formation, properly overlying 

 the Quartzite-dolomite ? — This, after all, is the most important question, 

 but I had no opportunities of studying it in the mountains of 

 Assynt. South of the line of Loch Borrolan there is an immense 

 change in the geological features of the country. The " Logan " 

 rock ceases to appear and the great range of Ben More seems to have 

 died away in the red syenite of Loch Borrolan, where it attains an 

 elevation of 1300 feet in Cnoc-na-Sroine. Most people regard this as 

 an igneous intrusive rock, and such it probably is, though with a 

 strong affinity for "Logan" rock, which it most likely injects and 

 partly perhaps passes into. Anyhow the great eastern chain of 

 Assynt which I have endeavoured to describe fails to the south of 

 this line. 



An important extension of the Upper Gneiss to the westward at 

 moderate elevations is the immediate result, and we are thus enabled 

 to see the stratigraphical relations of this group to the Quartzite- 

 dolomite under favourable conditions. Allusion has already been 

 made to the section at Craig-a-Knockan. If to see is to believe, 

 there ought not to be much difficulty here. The Quartzite sweeps 

 steadily down from Coul More, and is succeeded in ascending order 

 by the " yellow beds," and these by the Dolomite, the whole having 

 moderate easterly dips, just as is shown in Professor Geikie's section.^ 

 The junction with the Upper Gneiss, which succeeds, seems perfectly 

 regular, the direction of dip being still about the same and not 

 exceeding 10°. In the place where we saw the junction, along the 

 line of which we walked for some distance, there are no appearances 

 such as would justify Nicol's interpretation. In one place the Upper 

 Gneiss is very much crushed and full of pyrites, but there is 

 certainly no turning-up of the Dolomite, which may be seen for some 

 distance to underlie the so-called Upper Gneiss conformably and at 

 a moderate angle. It is for the students of Archaean geology to 

 upset the plain evidence of this section, which certainly seems to 

 mean what it says. Indeed, the beds hereabouts slope at such a 

 moderate angle, and there are so few signs of dislocation, that one is 

 scarcely prepared for an inversion, such as may well occur in the 

 troubled region of Ben More. 



There is only one other place where I had an opportunity of 



1 Q.J.G.S. vol. xvii. p. 180. 



