page 345 note * In his “Silurian System” 1839).

page 346 note * “Quart. Journ. Geol. Soc.” vol. xii. p. 38Google Scholar.

page 346 note † “Monograph on Fossil Estheriæ” (Palæontographical Society), p. 22Google Scholar.

page 346 note ‡ “Quart. Journ. Geol. Soc.” vol. xxvii. (1871), p. 241Google Scholar.

page 347 note * “Quart. Journ. Geol. Soc.” vol. xv. p. 493et seq.Google Scholar; and “Siluria,” 4th edit. p. 250.

page 347 note † “Quart. Journ. Geol. Soc.” vol. xvi. (1860), p. 312Google Scholar.

page 347 note ‡ See “Explanation to Sheets 160, 161, 171, and 172 of the Geological Survey of Ireland” (1863). It is much to be wished that some fossil evidence could be obtained to fix the limit of the Upper Silurian series in the south-west of Ireland. The lithological argument seems to favour the classification adopted by Mr Jukes, for a great part of his Dingle beds would answer well for much of the Lower Old Red Sandstone.

page 348 note * Salter, , “Quart. Journ. Geol. Soc.” vol. xix. p. 493Google Scholar.

page 348 note † Dawson, J. W. on “Fossil Plants of the Devonian and Upper Silurian Formations of Canada.” Geol. Survey of Canada Memoirs,” 1871, p. 10CrossRefGoogle Scholar.

page 350 note * Silurian rocks underlie the whole of Ireland, and appear at innumerable points throughout the island. In Scotland, likewise, they extend over the whole kingdom, save in a limited tract in the north-west. Their united area in the two countries cannot be less than 50,000 square miles. Their spread in England and Wales cannot be so easily determined, owing to the breadth of ground covered by later formations. But it must at least amount to 10,000 square miles, and probably is greatly more. Of course the Silurian rocks likewise extend under the sea in all directions. But this prolongation is not taken into account in the above calculations.

page 352 note * “Quart. Journ. Geol. Soc.,” vol. xix. (1863) p. xxxviGoogle Scholar.

page 356 note * “Beiträge zur Kenntniss Norwegens,” vol. ii. p. 118Google Scholar, et seq.

page 357 note * “Trans. Geol. Soc.” 2d ser. vol. ii. p. 125Google Scholar.

page 358 note * “Trans. Highland Soc.” new series, vol. v. p. 417Google Scholar.

page 361 note * “Quart. Journ. Geol. Soc.” xv. p. 400Google Scholar; and “Siluria” 3d edit 1859, p. 284Google Scholar.

page 361 note † “Quart. Journ. Geol. Soc.” xix. 493Google Scholar.

page 364 note * “Journ. Acad. Nat. Sci. Philadelphia,” vi. 2d series (1860–1869), p. 207Google Scholar.

page 366 note * “Siluria,” 4th edit. p. 362Google Scholar.

page 374 note * In the field observations from which I have plotted this table, I was materially aided by Mr B. N. Peach, whose active and helpful co-operation I would again heartily acknowledge.

page 375 note * When walking along the summits of the cliffs in Caithness and Orkney, I have often been struck by the evidence of the enormous force of the wind, which, caught in the clefts of these precipices, and converging upwards as in so many funnels, sweeps across the bald and barren ground at the top.

This evidence was more particularly striking in an examination (made in company with my colleague, Mr B. N. Peach) of the summits of the magnificent precipices which on the west side of Hoy rise vertically from the Atlantic breakers to a height of more than 1300 feet. Back from the broken and ruinous summit the ground is covered with a coating of peat, heather, and coarse grass. Over the growing vegetation abundant fragments of sandstone are scattered for a distance of many yards from the edge of the cliff. The larger pieces are chiefly flat, and may weigh a pound or more. On lifting them the vegetation underneath was found to be quite green, indicating that they had been only recently deposited. They are evidently torn by the wind, partly from the crumbling sandstone strata of the cliff, partly from holes which have been worn through the peaty and heathy soil, and they are moved up the slope by successive powerful gusts. Further proof of the force of the wind is furnished by the number of little pools, ponds, and miniature tarns scattered over the ground above the edge of the cliff. The wind, taking advantage of hollows and little gullies or holes worn in the peaty covering by runnels formed after heavy rain, tears them wide open. When in dry weather the surface of peat becomes loose and powdery, the dust and loose fibres are blown away. This, of course, takes place more especially on the sides and bottoms of the hollows, which are thus further widened and deepened. The return of heavy rain serves to fill these hollows with black or brown peaty water. But the denuding influence of the wind does not cease, for the water is thrown into ripples and waves, which, beating against the black peaty sides of the pools, loosens them and removes the peat, partly in solution and partly in suspension, so as to allow of its being carried away in the outflow. In this manner the ground comes to be covered with shallow ponds and sheets of black water, which remain until they are either filled up with decayed peat débris, or emptied by the lowering of their margin at the point of exit.

page 378 note * “Siluria,” 4th edit. p. 256Google Scholar.

page 381 note * Some remarkably steep angles of repose for the detritus of the mountain are to be seen on the south and east slopes, the angle seldom falling below 27° and rising sometimes to 35°, as measured by my colleague, Mr John Horne, who accompanied me in the ascent. The north and west sides are precipitous.

page 383 note * “Trans. Geol. Soc.,” 2d series, vol. iii. p. 127Google Scholar.

page 383 note † “Trans. Highland Society,” vol. vii.

page 383 note ‡ The tradition, so commonly told in such districts, is repeated here, of a dog having fallen into one of the subterranean passages, and having worked its way underground until, after some days, it succeeded in crawling out at an opening on the opposite side, but devoid of its hair, which had been scraped or shaved off by the rough walls of the narrow passages through which it had to force its way !

page 384 note * Op. cit.

page 389 note * “Quart. Journ. Geol. Soc.” vol. xiv. p. 72Google Scholar, and plate v. fig. 6.

page 392 note * “Quart. Journ. Geol. Soc.” vol. xv. p. 402Google Scholar.

page 394 note * Murghison, , “Quart. Journ. Geol Soc.” vol. xv. p. 403Google Scholar.

page 395 note * “Trans. Geol. Soc.,” 2d ser. vol. iii. See also Murchison, , “Quart. Journ. Geol. Soc.” vol. xv. p. 403Google Scholar.

page 395 note † “Trans. Highland Society,” vol. vii.

page 397 note * Op. cit p. 131.

page 398 note * The existence and effect of this fault were noted by Sedgwick and Murchison, op. cit. p. 133. In his later memoir, on the “Succession of the Older Bocks in the Northern Highlands,” Murchison, as stated above, referred to the locality as one where the flagstones pass under the overlying yellow sandstones, and he actually gives a section showing the conformable superposition of the latter strata upon the former. (“Quart. Journ. Geol. Soc.” xv. 409Google Scholar.)

page 400 note * “Quart. Journ. Geol. Soc.” xv. 402Google Scholar.

page 400 note † This was noticed by Sedgwick, and Murchison, , “Geol. Trans.” 2d ser. vol. iii. p. 134Google Scholar.

page 402 note * “Vieux Grès Rouge” p. 120. His specific name was recurvus.

page 404 note * I cannot distinguish between this species and a Glyptolepis. On mentioning this to my friend Dr Traquair, he fully corroborated my suspicions, and said that he believed it to be only G. leptopterus.

page 405 note * Dawson on Fossil Plants of Devonian Rocks of Canada, “Memoirs of Geol. Surv.” Canada, 1871.

page 406 note * I supplied Dr Heddle with a piece of this remarkable augite for analysis. His determination of its composition and my description of its occurrence will be found in his paper published in this tolume.

page 407 note * “Mineralogy of the Scottish Isles” vol. ii. p. 252Google Scholar. See also Neill's, P. “Tour in Orkney and Shetland” 1806Google Scholar.

page 407 note † “Synopsis of Classification of British Palaeozoic Bocks,” &c., 1855, p. 579Google Scholar, et seq.

page 407 note ‡ “Quart. Journ. Geol. Soc.” xv. 410Google Scholar.

page 407 note § These subdivisions had been noticed before by DrMaloolmson, (1839, “Quart. Journ. Geol. Soc.” vol. xv. p. 336Google Scholar) and by Millar, Hugh (“Footprints of the Creator,” p. 2)Google Scholar.

page 409 note * Op. cit. p. 410.

page 410 note * SirMurchison, R. (“Quart. Journ. Geol. Soc.” vol. xv. p. 410)Google Scholar, in describing the conglomerate of Stromness, refers it without question to the same basement position as the lowest conglomerates of Caithness. He likewise speaks of the red sandstone of Kirkwall as occupying a similar low horizon. Further examination, however, would have shown that these sandstones not merely underlie, but are interstratified with and overlie flagstones. The coarse conglomerate of well-rounded sandstone blocks at Heglabir on the west side of Sanday, which has been long known (see Barry's, “Orkney,” p. 56Google Scholar, and Neill's “Tour”), seems to occur at a greater distance from the local base, for it is said to overlie sandstones and flagstones. (See ante, p. 409.)

page 411 note * “Quart. Journ. Geol. Soc.” xv. p. 404Google Scholar.

page 414 note * See Jameson, , “Mineralogy of the Scottish Isles” (1800), vol. ii. p. 186Google Scholar; Traill, in “Neill's Tour in Orkney and Shetland,” 1806Google Scholar; Fleming, , “Memoirs of Wernerian Society,” vol. i. (1808), p. 162Google Scholar; and in Shireff's, “Agriculture of the Shetland Islands” (1814), p. 120Google Scholar; Hibbert, , “Description of the Shetland Islands” (1822), p. 157Google Scholar.

page 418 note * “Quart. Journ. Geol. Soc.” vol. ix. p. 49Google Scholar.

page 418 note * Murchison, , “Quart. Journ. Geol, Soc.” xv. p. 413Google Scholar.

page 418 note † See Hooker, Ibid. ix. p. 49.

page 418 note ‡ “Mem. Wernerian Soc.” vol. i.

page 420 note * Jameson, (“Mineralogy of Scottish Isles,” ii. 207)Google Scholar speaks of the “wacken” (felstone) lying upon a kind of breccia at the north end of the island, and traversed by veins of greenstone and basalt.

page 422 note * After the visit to Shetland, of which the results are given above, my former pupil, Dr George A. Gibson, at my suggestion, undertook a further examination of the Old Red Sandstone of these islands, and prepared an essay on the subject, which he submitted to the Senate of the University of Edinburgh as his thesis previous to presenting himself for examination for the degree of Doctor in Science. Since the foregoing pages were written, the essay has been published, and I am glad of this opportunity of referring to it. He has traced the faults with care, and has extended his observations to Foula, where he finds red and grey sandstones similar to those of Shetland rising into the vast sea-precipice for which this island has long been famous. See his “Old Red Sandstone of Shetland.” Edinburgh, 1877. [See note appended to the present Memoir.]

page 422 note * See Miller's, Hugh “Old Red Sandstone,” 4th edit. p. 54Google Scholar, note.

page 423 note * Malcolmson, , “Quart. Journ. Geol. Soc.” xv. p. 350Google Scholar, footnote, where a brief reference to the order of succession of the strata is given.

page 423 note † Op. cit. p. 432.

page 424 note * It was from these nodules that Dr Gordon obtained the fossils already referred to. He informs me, however, that no record seems to have been kept of them, and that he cannot say what were the species.

page 425 note * Since this was written another volcanic locality has been found. See p. 435, note.

page 425 note † Murchison, , “Quart. Journ. Geol. Soc.” xv. 432Google Scholar.

page 426 note * “Trans. High. Soc.” vol. vii.

page 428 note * See Boué, , “Essai,” p. 101Google Scholar.

page 428 note † “Trans. Geol. Soc.” 2d series, vol. ii. p. 363Google Scholar.

page 428 note ‡ “Trans. Geol. Soc.” (1835), 2d series, vol. v. 145Google Scholar.

page 428 note § “Quart. Journal Geol. Soc.” xv. 349Google Scholar. Read in 1839.

page 435 note * Since my description of the Old Red Sandstone of these northern regions was written, the work of the Geological Survey has commenced in that area. Mr J. G. Wilson, who has been intrusted with the mapping of the district above referred to, has made the interesting discovery of a bed of diabase-porphyrite, interstratified in the lower part of the section of sandstone and conglomerate in the Gollochy Burn, near Buckie. This is a true lava-flow; he has observed pebbles of the rock in some of the overlying strata. With the exception of the Rhynie diabase already referred to, it is the only example yet noticed of the occurrence of contemporaneous volcanic rocks in the Lower Old Red Sandstone on the north side of the Grampian mountains, until we reach the far distant Shetland Islands. I have examined it microscopically, and find it to be identical in character with some of the lavas of the Lower Old Red Sandstone of central Scotland. It has a characteristic porphyry ground-mass through which are scattered decayed plagioclase crystals and numerous opaque ferruginous pseudomorphs, many of which appear to represent former augite. The characters of the volcanic rocks of the Old Red Sandstone will be described in a subsequent portion of this Memoir. [Since this Memoir was read I have had an opportunity of examining the locality where this volcanic sheet occurs, and of confirming the view taken of its relations by Mr Wilson. If we may judge from the different petrographical aspects of the mass, it would seem to consist of more than one flow, but with no intercalated tuff or other strata..]

page 436 note * Malcolmson, op. cit p. 346.

page 436 note † See Malcolmson, op. cit. p. 345.

page 437 note * “Quart. Journ. Geol. Soc.” xv. p. 425Google Scholar.

page 438 note * Op. cit. p. 425.

page 438 note † Malcolmson, , “Quart. Journ. Geol. Soc.” xv. p. 344Google Scholar. [Since this paper was read I have had an opportunity of examining the collection of Old Red Sandstone fishes in the Museum of Practical Geology, Jermyn Street. In the “Catalogue of Fossils” published in 1865, three specimens of Asterolepis are marked as occurring, two of them in the Upper Old Red Sandstone of the Moray Firth, and one in that of the Heads of Ayr. Being convinced that no Asterolepis was likely to have been obtained from those localities, I was gratified to find on inspection that one of the specimens was a fine plate of Pterichthys major, and that the others were Holoptychius scales—fossils eminently characteristic of the Upper Old Red Sandstone. My colleague Mr Etheridge at once acknowledged that the fossils had been erroneously entered in the catalogue. No doubt much of this confusion may be traced to the fault of the original synonymy. The Asterolepis of Eichwald and Pander is the Pterichthys of Agassiz; the Asterolepis of the latter naturalist is equivalent to the Homosteus of Asmus and Pander.]

page 439 note * “Edin. New. Phil. Journ.” new series x. p. 29Google Scholar, et seq.

page 439 note † “Quart. Journ. Geol. Soc.” xv. p. 424Google Scholar.

page 439 note ‡ See Murchison, , “Quart. Journ. Geol. Soc.” xv. p. 423Google Scholar.

page 442 note * Op. cit p. 338.

page 442 note † [Since this was in type Mr Horne has extended the work of the Geological Survey into the Findhorn district, and has traced the unconformable overlap of the Upper Old Red Sandstone.]

page 443 note * See their Memoir, “Trans. Geol. Soc.” 2d ser. iii. 147Google Scholar.

page 444 note * Op. cit p. 146.

page 445 note * “Old Red Sandstone.” Plate of Sections, figs. 4 and 5.

page 445 note † Op. cit. p. 150.

page 445 note ‡ “Quart. Journ. Geol. Soc.” xix. p. 507Google Scholar.

page 445 note ‡ § Op. cit. XX. 437.