James Nicol

On the Geological Structure of the Southern Grampians

abstract The author stated that in 1844, and in subsequent years, he indicated that the Silurian strata of the South of Scotland are represented in the North by the metamorphosed or so-called primary strata; and he proceeded to point out that the object of the present communication is to examine the relation which the three great formations. Clay-slate, Mica-slate, and Gneiss, bear one to the other as regular constituents of the crust of the earth, and especially in certain parts of the Scottish Highlands, as illustrated by sections observed by himself. These he correlated with what is seen in other parts of the Highlands. He also stated that, both in former papers and in his published map, he has always regarded the gneiss of the west coast and certain mica- or chlorite-slates of the interior as identical only so far as both belong to the great series of metamorphic formations inferior to the red sandstone and quartzite, but still as distinct formations with peculiar features, and, it may be, of widely different age.

On the Structure of the North-Western Highlands, and the Relations of the Gneiss, Red Sandstone, and Quartzite of Sutherland and Ross-shire

Before concluding, I must state that, even had it been proved that the mica-slate or fine-grained gneiss of Sutherland truly overlaps the quartzite, and that this overlap is the result of subsequent deposition, the fact would not bear out the conclusions that have been deduced from it, or establish that entire revolution in Scottish geology which has been supposed. Proof would still be wanted that the mica-slate of Loch Erriboll and Loch Hope is inferior to the great masses of granitic gneiss in the centre of Sutherland. We might ask for a continuous section through the interminable moors of the Moin, and for evidence that the Kyle of Tongue and the huge syenite domes of Ben Laoghal and Ben Stomino do not break the series and bring up anew the lower and older gneiss. But such continuous sections have never even been attempted, either there or through the wilds of Assynt and Strath Oykill, still less across the mountain-fastnesses of the Dirry Moor and Fannich Forest, so as to assure us that no older underlying gneiss comes up there. Till this is done, there is no evidence to connect the great mass of crystalline schists stretching from the north coast of Sutherland to the south of Inverness-shire more closely with the mica-slates of Ben Hope than with the gneiss of Scourie, Loch Inver, and the Gairloch, or to justify us in throwing aside mineral characters for some assumed synchronism in the age of the original, but now wholly altered, deposits.

On the Parallel Roads of Glen Roy

The general characters and appearance of these celebrated roads are so well known as scarcely to require to be mentioned. Running apparently with perfect horizontality and complete parallelism along the two sides of a long Highland glen, turning up every lateral valley and encircling every hill, they form a spectacle altogether unique in this country, and which, when once seen, can never be forgotten. Their mode of origin, on the other hand, still remains one of the open, undecided questions in Scottish geology. Various theories have been proposed, each enjoying popularity for a time, but no one permanently remaining master of the field. The horizontality, parallelism, and general character of the lines leave no doubt that they have been formed by water standing at the level of each line or road for a very considerable period, and then suddenly subsiding to the level of the next lower road. Thus far all recent observers seem agreed. But fresh water and salt—mountain loch and sea-firth—have still each their own supporters; and some who once advocated the one of these views, may now be found supporting the other. It is thus evident that no facts very decisively in favour of either theory have yet been adduced. But that such facts do exist I hope to be able to show in the following observations, and thus to contribute some evidence tending to decide this question. As the general aspect and characters of these lines or roads are so well known, and have been so

On the Geology of the Southern portion of the Peninsula of Cantyre, Argyllshire

The peninsula of Cantyre forms one of the most anomalous features in the physical conformation of Scotland, whether we regard its geographical or geological peculiarities. The mountain ridges which give their character to other parts of the country have all, more or less, a direction from north-east to south-west. On the other hand, this peninsula runs nearly north and south from the Crinan Canal to the Mull, a distance of fifty-five miles, with an average breadth of only six to eight miles. It thus forms a narrow ridge of no great elevation, separating the Firth of Clyde from the open expanse of the Atlantic, whose waves during storms from the west heat with awful fury on its western shores. None of its mountains rise high, and in some places it is almost separated into several islands by low transverse valleys. Thus at Loch Tarbet the isthmus is only about a mile in breadth, and both there and at Campbeltown a depression of a few feet would convert it into several detached islands ; which was probably its condition at no very remote geological date. Although forming a portion of the Scottish Highlands, its termination lies further south than some parts of the north of England.

Observations on the Silurian Strata of the South-East of Scotland

During a visit to the south of Scotland last autumn I collected some fossils from the older rocks of that district, which appear interesting as adding another link to the chain of evidence by which the true age of these deposits may he ascertained. Taken in connection with the fossils formerly noticed* and with those procured by Mr. Moore in Wigtonshire†, they may be regarded as rendering the Lower Silurian age of one part of these beds almost certain, so that the connection of the rocks and mountain-chains of this portion of Britain with those of other countries may now be so far traced out. The fossils which Mr. Salter last year kindly determined were chiefly procured from the only bed of limestone known in the Silurian rocks of the south-east of Scotland. My hopes of obtaining better or more characteristic specimens from that locality were disappointed, and not even a single new form was discovered after a careful search. Indeed, the highly crystalline texture of the limestone, probably occasioned by a mass of trap with which it is always associated, renders it very improbable that this bed will ever add much to our knowledge of the beings existing in the seas in which it was deposited. My researches in the slate rocks were more successful, especially in the Grieston quarry near Traquair. In this place the rocks consist of clay-slate, sometimes passing into a fine greywacke, and are wrought for a coarse kind of roofing-slate. The strata are thin

On the Geology of the Silurian Rocks in the Valley of the Tweed

There is perhaps no extensive formation in the British Islands of which we possess less certain geological knowledge, than of the rocks constituting the great mountain-chain which crosses the southern counties of Scotland from east to west. These deposits have indeed been long ascertained to be of far more ancient date than the old red sandstone and carboniferous rocks with which they are in contact; and from this and their mineralogical characters have usually been classed in the transition series of Werner, and more recently placed hypothetically on the parallel of one or other portion of the Silurian rocks of England. This very uncertain determination of their age has in a great measure arisen from the extreme rarity of their fossil remains, which till very lately were scarcely known to exist. Having in the course of last autumn succeeded in procuring a few specimens of organic remains from the central portion of this formation, in the upper part of the valley of the Tweed, I have thought that a notice of these may not be without interest to the Society. With this I shall combine some observations on the mineralogical character and position of the rocks in this district, and the indications which these afford of the geological age of the formation and the conditions under which it has been produced.

How the Parallel Roads of Glen Roy were formed

In a paper on the “Origin of the Parallel Roads of Glen Roy,” read before the Society and published in the Quarterly Journal for August 1869, I described some physical facts which appeared to me to place their marine origin beyond doubt. So far. as I am aware, no attempt has been made to answer that argument. But I have been asked “to explain the extraordinary coincidence of the sea-level with five (four) successive cols.” It has been further asked how, if the same sea filled Glen Roy and Glen Gloy, it formed a road in the latter and none in the former glen; why are the lines of partial occurrence even in this region—the highest limited to Glen Gloy, the second and third almost to Glen Roy, whilst the fourth extends round both Glen Roy and Glen Spean? If all the time the same sea filled all these glens, and was liable to the same oscillations of level, why has it formed roads in one or two of them only, not in all? Why are not the second and third roads as well seen in Glen Spean as in Glen Roy, and the Glen-Gloy line not in one only but in all the three? These questions plainly need to be answered; and the answer, in my opinion, forms the key to the whole of the phenomena. Facts stated in my former paper proved that, shortly before the formation of the roads, this part of Scotland was submerged in the

On the Slate-rocks and Trap-veins of Easdale and Oban

In the Geological Map of Scotland a narrow band of clay-slate is laid down as skirting the eastern shore of Islay and Jura, and passing through Luing and Seil to Kerrera and the vicinity of Oban. This rock was fully described by Dr. Macculloch in his work on the Western Isles; and I should not have noticed it further, had not my observations led me to differ from him in some important points. My present remarks refer, however, only to this formation as seen on Seil and Easdale and in the vinity of Oban, and more especially to the former locality. This place has been long celebrated for its extensive slate-quarries, the property of the Marquis of Breadalbane. These works give employment to about 200 persons. They are chiefly situated in the small island of Easdale; and, the higher parts of the rock being exhausted, they are now carried on at a great depth below the level of the sea. Mineral character of the rocks.—The slates extracted for roofing-purposes on Easdale and Seil are usually dark-blue or almost black, with a silky lustre. They are split along true planes of cleavage; but the thin laminæ are uneven and undulating. Their surfaces are thus often striated or wrinkled, similarly to what is named ripplemark in other beds, but in this case clearly produced in an entirely different manner. Crystals of iron-pyrites (usually cubes, but with one axis often abnormally shortened) are dispersed in more or less abundance through these slates. As

On the Newer Red Sandstone, and on some other Geological Phenomena, near Loch Greinord, in Ross-shire

In several passages of his work on the Western Isles, Dr. Macculloch refers to the occurrence on the shores of Loch Greinord of two small spots of a red sandstone of newer age than the great mass of similarly coloured rock which forms so conspicuous a feature on the western coasts of the Highlands. In his memoir on the Geological Map of Scotland he also several times mentions this formation, which he considered as the only undoubted instance of the occurrence of the “Red Marl” of English geologists in the northern part of the island. Although evidently regarding these beds with much interest, he has not given any detailed description of them. In their valuable memoir on the formations in the North of Scotland, Professor Sedgwick and Sir Roderick I. Murchison likewise mentioned this deposit, and pointed out its resemblance to the New Red of England, and also to some beds seen below the Lias in Skye. This sandstone does not seem to have been subsequently noticed by geologists, probably from lying in a region so seldom visited by the scientific traveller. I have therefore been induced to lay before the Society the following notes collected in an examination of this deposit in the autumn of last year (1856). The great headland of the Ruimore or Ru Rea that separates Loch Greinord from Loch Ewe consists chiefly of the older red sandstone of the west coast, covered more or less deeply by drift or detritus. On the shore of Lake

Notice of the Occurrence of Coal near Erzeroom

An extensive seam of coal has been discovered in the district of Oltoo, about thirteen hours distant from Erzeroom. The coal is stated not to be of prime quality, containing a good deal of sulphur; and it is slaty, leaving a residue, probably of 12 to 15 per cent. The seam is represented as very broad, and situated on the side of a hill, so that at present it can be worked for the mere labour, and a man in a day can work out 600 okes, or about three-quarters of a ton.