86 REPORT — 1855. 



cation, entitled 'Siluria,' Sir Roderick called the special attention of the Section to 

 the consideration of the true relations of these deposits to the crj'Stalline rocks of 

 the Highlands. To satisfy his mind on this point, and to see if it was necessarj' to 

 make any fundamental change in his former views, the author re-surveyed his old 

 ground in Sutherland, Caithness, and Ross-shire, accompanied by Prof. James Nicol. 

 Obtaining ample evidence to induce him to adhere to his former opinion, that all the 

 crystalline rocks of that region, consisting of gneiss, mica-schist, chloritic and quartz- 

 ose rocks, limestones, clay-slate, &c., were originally stratified deposits, which had 

 been crystallized before the commencement of the accumulation of the Old Red Sand- 

 stone, he first gave a rapid and general sketch of those ancient rocks, whose cry- 

 stalline character he attributed to a change of their pristine sedimentary condition. 

 They have a prevalent strike, varying from N.E. and S.W. to N.N.E. and S.S.W., 

 and in the northernmost counties of Scotland their usual inclination is to the E.S.E. 

 or S.E., usually at high angles. 



In combating a theoretical idea, which had recently been applied to the crystalline 

 rocks of Scotland, viz. that many of their apparent layers Were simply a sort of 

 crystalline cleavage, by which the different minerals were arranged in parallel folia 

 or laminae, and were independent of the original lines of deposit, he showed how 

 the geologists who had longest studied these rocks in Scotland had formed a different 

 opinion. Hutton, Playfair, Hall, Jameson, M'Culloch, and Boue, all believed, as 

 ■well as Professor Sedgwick and himself, that the variously constituted and differently 

 coloured layers of these rocks truly indicated separate deposits of sand, mUd, and 

 calcareous matter. He also cited numerous cases of interstratified pebble beds and 

 limestones as completely demonstrative of their original status. Alluding to the 

 real distinction between stratification and cleavage, he expressed his belief that, 

 whilst in scarcely any part of the Highlands which he had seen, did there exist that 

 perfect and symmetrical cleavage which prevails in North Wales, there Was, never- 

 theless, a very marked and prevalent division of these Highland crystalline rocks into 

 rhombic and other forms by rude cleavages and decisive joints. 



In describing two traverses which he made across these crystalline rock masses 

 in the north coast of Sutherland, — the first, twenty-eight years ago, the other in the 

 ■weeks preceding this meeting, — and, in mentioning with dU6 praise a memoir, of 

 intermediate date, by the late Mr. Cunningham, it was stated, that the oldest, or 

 lowest visible stratified rock in that region was a very hard, gray, qUartzose gneiss, 

 traversed by veins of granite, as seen on the shores of Loch Laxford, Cape Wrath, 

 the escarpment of Ben Spionnach, in Durness, and other places. 



At the last-mentioned locality, and near Rispond, tlie older gneiss is uncohform- 

 ablv overlaid by a copious series of quartz rocks, of white and gray colours. Occa- 

 sionally passing into mica-schists or flagstones, and also into stratified masses, Which 

 are also gneissose, inasmuch as they are composed of quartz, mica, or felspar. With a 

 copious interstratification of bands of limestone, near their lower parts, these crystal- 

 line rocks are very clearly exhibited between Loch Durness and the Whiten Head on the 

 coast, or between Ben Spionnach and Loch Eribol in the interior. It is in one of the 

 beds of limestone subordinate to the lower quartzites of this great series, at Balnakiel, 

 in Durness, that Mr. Charles Peach recently discovered organic remains; and, as their 

 discovery has led to certain suggestions, including one which would refer these cry- 

 stalline rocks to the Devonian or Old Red Sandstone formation, the author shows 

 ■why such an opinion is untenable. For, whether a section be made across the 

 various strata between Loch Durness and Loch Eribol, or from the latter to Loch 

 Hope, the same limestones, subordinate to quartz rocks of white and gray colours 

 (including some rare coarse white grits, as in the summit of Ben Spionnach), and 

 associated with many siliceous concretions (of various colours, red and dark gray), 

 are distinctly and conformably overlaid by and pass up into micaceous quartzite and 

 dark-coloured schists, both chloritic and talcose, which are followed by other and 

 differently composed stratified masses, having the character of gneiss. Along the 

 north coast, these overlying masses extend to the west shore of Loch Tongue, before 

 they are interfered with by any mass of granite; and it is therefore unquestionably 

 true, that the band of limestone containing the fossil shells discovered by Mr. Peach 

 is a low member of this great crystalline series of stratified rocks of such diversified 

 characters. 



