374 PEOCEEDINGS OF THE GEOLOGICAL SOCIETT. [DeC. 1, 



and in the Bealloch oi* depression between the grand mountains of 

 Fionavin and Meal Horn, — ^the former composed of the lower quartz 

 resting on old gneiss, the latter of the overlying flaggy and micaceous 

 series. The limestone occupies a similar geological position to the 

 east of Arkle and Ben Stack. There, though only visible at intervals 

 through the thick covering of peat and heather of a deer-forest, the 

 beds of limestone are to be observed dipping steadily to E.S.E. and 

 quite conformably to the underlying quartz-rock, wMch slopes down 

 in brown masses from the shoulders of Arkle and Ben Stack ; the 

 former exhibiting noble white precipitous faces on the S.S.W. The 

 banks of Loch Stack and Loch More, extending from N."W". to S.E., 

 naturally expose transverse sections of this regular succession from 

 the fundamental gneiss through this overlying Lower Silurian series, 

 — ^the Cambrian rocks having again thinned out and disappeared, as 

 in Durness. 



Ascending the mountain of Ben Stack, 2363 feet high, we found 

 that the old gneiss, of which the mass is composed, was covered by a 

 pebbly band, which formed the base of the quartz-rock, and passed 

 eastwards into overlying sheets of the same ; and these, on both the 

 north and south shores of Loch More, are covered by thin bands of 

 limestone, which in their turn, and particularly on the south side, 

 are followed by siliceous flagstones, occasionally used for building, 

 while to the north some of these rocks are used as hone-stones. 

 Nowhere, in short, in all this range, is the limestone placed in a 

 trough by a reversed dip, as in Durness, all the strata being inva- 

 riably inclined to the E.S.E., whilst the masses lying to the east, 

 though occasionally gneissic, are on the whole very different from 

 the old or fundamental gneiss. 



The limestone reappears in its course to the S.S.W. at the head of 

 the Lochs of Glendhu and Glencoul, and thence passes into Assynt, 

 where it again expands, as in Durness, into a mass of considerable 

 thickness, and is there more clearly exposed between masses of 

 quartz than in most parts of its northern range. 



Fossils of the Durness Limestone.- — Mr. Saltek has supplied me 

 with the following description of the Organic Eemains from the 

 Durness Limestone. 



CEPHALOPODA. 

 Oethoceras meitdax, spec. nov. PI. XIII. fig. 24. 

 This form comes nearer to Hall's figures of Orthoceras multicame- 

 ratum (Pal. New York, vol. i. pi. 11) than to any other species we 

 are acquainted with ; and as the smooth Orthoceratites are so difficult 

 to identify, it would have been more satisfactory to me to have left 

 it with that species, than propose a new specific name. But in the 

 adult portion of our shell there is an appearance of annulation, which 

 cannot be altogether due to the state of the fossil, for it is too 

 regular ; the younger portion, in an equal state of preservation, ap- 

 pears quite smooth. The contradictory appearances have suggested 

 the name. 



