1858.] MUECHISOIf NOETHEEN HISHIAISDS, ETC. *373 



able ascending section from the fundamental gneiss, which ranges 

 from Ben Spionnach to Loch Soan on the west side of Loch Eribol. 

 For he there sees the lower quartz-rock dipping to the E.S.E. from 

 off the shoulders of the older gneiss hills, and even from the summit 

 of Ben Spionnach, 2204 feet above the sea, and then plunging under 

 the limestones of Island Chorrie and Eribol, as described on a 

 former occasion. 



As it had been doubted by Professor Nicol whether the quartz- 

 rock which I had described as regadarly overlying in some places 

 the limestone of Diurness, Eribol, and Assynt was not cut off from 

 the latter by dislocations, I especially explored, in my last visit, the 

 coast-ridge on the west side of Loch Eribol from the Ferry to 

 the north. In that direction, or in the northerly strike of the beds, 

 the limestone, which at first occupies several low hills resting upon 

 the lower quartz which flanks the sea, thins out gradually to a very 

 small band which under Cnoc Craggin and to the north of Heilam 

 is seen to be fairly interpolated between the lower and a band of 

 upper quartz-rock, — the latter being pure white, and all the strata 

 dipping to the E.S.E. at about 18°. 



In the hills extending towards the Whiten Head, where all the 

 strata are exposed on the sea- cliffs, we pass over, in ascending, first 

 the upper beds of the lower quartz-rock, charged with the Anne- 

 Kde-tubes and the SerpuUtes Maccullochii, and graduating up into 

 the limestone by impure calcareous strata, and then the limestone 

 itself with Fucoid-shale. Now aU these beds of quartz-rock and in- 

 cluded limestone are, I maintain, covered, as a whole, by the mica- 

 ceous flagstones, schists, and younger gneiss of the higher hills, and 

 these clearly extend to the Kyle of Tongue and the flanks of Ben 

 Hope. The last-mentioned lofty mountain is indeed almost en- 

 tirely composed of such micaceous flagstones (d of the sections), all 

 of which have hitherto been mapped under the name of gneiss. The 

 strata on the west shore of the Kyle of Tongue are literally almost 

 sandstones. 



In this way I not only satisfied myself that the section of 1827, 

 showing a yoimger micaceous and gneissose flag-stone series over the 

 limestone of Durness and Eribol, was correct, but also that the 

 latter, like many other Silurian limestones, was an accidental de- 

 posit, subordinate to a great siliceous or quartzose series. In fact, 

 the limestone, so expanded at Durness as to occupy a wide basin, as 

 well as on the large island of Hoan, thins out and disappears in a 

 quartzose series as we proceed from Eribol towards the Whiten 

 Head or the N.N.E. 



In its longitudinal range from Loch Eribol to the South of Assynt, 

 or for a distance of about forty miles from N.IS'.E. to S.S.W., the 

 limestone performs precisely the same part, showing itself occasion- 

 ally in thin courses only, either pinched out or scarcely traceable, 

 but always fairly intercalated in the quartzose and crystalline 

 rocks. 



Thus, when not covered by moss and heather, the limestone crops 

 out at several spots to the S.S.W., as at the head of Loch Eribol 



