1859.] MTTBCHISON NORTH HIGHLANDS. 229 



metamorphosed rocks are thrust about in dire confusion, connected 

 apparently with the great fault of Balnakealo Bay and associated 

 with serpentine. Prof. Harkness thought that he could here also 

 trace north and south faults. 



Now, whether or not the arrangement of the strata be found to bo 

 more or less in accordance with his view, my object is gained by 

 simply showing that, occupying a highly broken trough, the Durness 

 limestone is really proved to rest upon the lower quartz-rock, and 

 to be flanked, and indeed overlain, by the upper series of quartzose 

 and gneissosc rocks. The clear order of succession is, however, so 

 admirably seen on the shores of Loch Eriboll, that we may now 

 review the natural sections which are there exhibited. 



Section across Loch Eriboll to the adjacent country on the East.- — 

 Having been enabled, through the hospitality of my friend Mr. Alex. 

 Clark, of Eriboll House, to re-examine in detail the transverse sec- 

 tion across the escarpment where Prof. Sedgwick and myself observed 

 ( 1 827) the clear superposition of the micaceous flagstones, chlo- 

 ritic schists, and younger gneissic strata to the limestones of Loch 

 Eriboll, I have now the satisfaction of being able to produce some 

 important additional details, and to confirm the accuracy of my 

 general conclusions by the testimony of my companion Prof. Ram- 

 say, and also of Prof. Harkness, who has since visited these spots. 



In order, however, to convey to the reader a clear view of the 

 whole subject, I will call his attention, as in Assynt and at Loch 

 More, to the ascending order, as exhibited in a transverse section of 

 about ten miles in length (see fig. 7, p. 226). 



The fundamental or massive gneiss, which occupies the escarpment 

 of Pen Spionnach, and is well exhibited on the sides of a little loch, 

 and in the sides of the torrent (Alt-ach-na-cailk) running down 

 tut he Bridge of Grudie, is unconformably surmounted on its summit 

 by the bottom-beds of the lower quartz-rock, which, though not so 

 coarse as on the summit of Ben Stack, are still pebbly grits, the finer 

 beds of which might serve as millstones. These, cow red by a con- 

 siderable thickness of fine-grained quartz-rock, dip away to the E. 

 and K.S.E. into Loch Eriboll, the western bank of which is almost 

 entirely composed of them. The overlying limestone is Been in tho 

 Island of Chorrie, reappearing in force on the mainland at and above 

 the house of Mr. Clark, in ascending from which, to the summits of 

 the hills on the east, the clear order of superposition is exhibited 

 which is given in the preceding section (ti.u r . 7). and which ma> lie seen 

 over a breadth of two or three miles, particularly in the escarpments 

 and on the summits which lie in the north of the road ascending 

 from Eriboll Souse to altnaharrow. 



In comparing this section with that in Quart. Journ. Geol. Boo. 



vol. xv. p. :')^:'., of the same tract, it will 1 bserved that, whilst 



the general BUCCeSsion is identical, some important detaiU are now 



added. 



Thus, the limestone Which rises from the huh. and forms a sue- 



cession of terraces, is separated from an upper limestoi f much 



[ess thickness by a /one of quartz-rook, about 600 feel in thickness, 



