AIsTNIVEKSART ADDEESS OF THE PKESIDENT. 9 1 



as we pass over the outcropping edges of the apparent strata, 

 marked mineral differences, both macrosopic and microscopic, can 

 be noted, which seem to indicate a true succession in the beds, 

 which have thus been modified by subsequent pressure, and I am 

 inclined to think that the general strike of the two structures is the 

 same. The greatest crushing, the greatest shearing — in short, the 

 greatest modification — of the original constituents is at the northern 

 escarpment of the overthrust mass. On the summit of Craig Eoy 

 and in the upper part of Glen Docherty, these effects, though still 

 marked, are generally less extreme. It is, I think, possible to 

 infer the original character of the rocks from which this part of the 

 " newer gneiss " has been formed, viz. that they were rather fine- 

 grained gneisses, not very unlike those of Gairloch, occasionally highly 

 micaceous, but usually quartzose. I am certain that in none of the 

 sections that I examined was there any representative of the 

 quartzite series. It would no doubt be more difficult to distin- 

 guish an included and compressed fold of the Torridon Sandstone, 

 but I believe that I may with equal confidence deny its presence. 

 So far as I can judge from a more superficial examination, this 

 series of quartzose and micaceous rather than felspathic gneisses 

 extends for some miles southward and reappears in other parts of 

 Scotland, as do rocks undistinguishable from the somewhat more 

 coarse-grained varieties near Gairloch. 



Before leaving this subject, I may mention that we find a close 

 parallel to the " newer gneiss " series of the northern escarpment 

 on the southern edge of the crystalline massif of the Central High- 

 lands. In the cliffs north of Stonehaven the Old Eed Sandstone is 

 underlain * by an apparently bedded series exhibiting similar frag- 

 mental characters, and similar indications of partial metamorphism 

 to those which we observe in the northern cliffs of Craig Roy ; and 

 as we follow the shore northward the clastic character becomes less, 

 the metamorphic more marked, until at last we cannot doubt that we 

 are examining a series of fine-grained gneisses, although they still 

 exhibit some signs of subsequent crushing. This at Muchalls (some 

 three miles further north) is still less conspicuous, being sometimes 

 distinctly subordinate to the original foliation, to which it is often 

 inclined at a high angle. But, near Stonehaven the fissile structure 

 is occasionally so marked that the rock splits up like a slate. Other 

 masses, again, might readily be taken for compressed quartz-felspar 

 grits, like the Torridon Sandstone ; but careful work on the ground 

 after microscopic examination of specimens clears up the difficulties. 

 The dip of the apparent bedding is generally about I^.N.W., and 

 is usually pretty high, sometimes as much as 70°. Here also these 

 structures have a general correspondence with some marked mineral 

 changes in the rocks, and look as if, at any rate, the strikes of 

 the subsequent cleavage and the original bedding coincided. 



Microscoijic Structure of tlie Older ArcluPMU Rochs. 

 i^ot the least difficulty in the investigation of the most ancient 

 * The junction is a faulted one. 



