386 PEOCEEDINGS OF THE aEOLOGICAL SOCIETY. [DeC. 1, 



at Loch Craigie, and again at Lub-croy, these flaggy micaceous rocks 

 are well exposed, at the last-mentioned place assuming a gneissose 

 aspect. They are all perfectly conformable, all dipping steadily to 

 the S.E. or E.S.E., and are completely distinct, even in mineral 

 characters, from any of the underlying rocks, whether old gneiss, 

 Cambrian, or the quartzose and calcareous Lower Silurian group. 

 They are, in short, dark micaceous flagstones, which to the N.N.E. 

 range across the upper end of Loch Shin, and thence in the same 

 direction extend to Ben Hope until they occupy the expanse of 

 country between Lochs Eribol and Tongue. See fig. 8, p. 383. 



If the banks of the Oikel be descended until that river falls into 

 its marine estuary at Eonar Bridge, the succession of overlying and 

 conformable micaceous and other flagstones is equally clear until we 

 reach the edge of the true Old Eed Sandstone of the east coast, the 

 conglomerate base of which is formed out of the debris of aU the 

 rocks hitherto adverted to. 



If, however, the line of section be deflected from the Oikel a little 

 to the N.E. towards Lairg and the south-eastern end of Loch Shin, 

 then, the overlying flagstone and micaceous series being intruded 

 upon by vast masses of granite of posterior date, the depository beds 

 are so altered, veined, and fractui^ed as to be made to resemble in 

 some respects the old gneiss of the west coast. But these are local 

 exceptions ; for the observer has only to remove to a little distance 

 from the edge of the eruptive granite, to the S.E., and he again finds 

 himself in the same flaggy micaceous series as before, — all the beds 

 dipping to the S.E. and E.S.E. The amount of metamorphism pro- 

 duced upon these micaceous and quartzose flagstones, when they have 

 been most affected, is nowhere better exemplified than where they 

 wrap round the granitic and felspathic rocks of the Ord of Caithness 

 and the adjacent tracts, and where many beds constitute a sort of 

 gneiss, and others form, as before said, the completely metamorphosed 

 and crystalline quartz-rock of the Scarabin Hills (p. 384). 



Unwilling to generalize too far upon this point (for I have already 

 said that there may be many tracts where the oldest gneiss rises to 

 the surface), I may, however, express my present behef that these 

 micaceous flagstones (often used indeed as roofing- slates, though none 

 of them are affected by a true slaty cleavage), which constitute the 

 edge of the so-called primary rocks of Eoss-shire, and thence range 

 into Inverness, Nairn, Moray, and Banff, are parts of a series 

 younger than the fossiliferous Lower Silurian rocks of the west of 

 Sutherland. 



If it be objected that the great thickness of these masses offer 

 difliculties in the way of recognizing them to be equivalents of Silu- 

 rian rocks, I would reply that we have by no means proved that all 

 such beds are to be considered as successive, since the micaceous flags 

 may have been deposits in the same sea, but at some distance from 

 the bottom rocks ; and though apparently overlying them, may have 

 been of almost contemporaneous formation, their subsequent eleva- 

 tion and crystallization giving to them the appearance of a distinct 

 superposition. 



