4. The same, but divided by a thin vein of ochraceous matter, 10 140 From the bottom of the glen to the level of the house, From the house, to the level of the sea, about Total height of the mountain, 100 492 It appears then that, from the last measurement, in a distance not exceeding two miles, the range of the summit has gained, in elevation towards the west, 286 feet. All these sunk terraces have the plane of their strata reclined against the original mountain; that is to say, in sinking, their bases have been shoved beyond their perpendiculars. From this angularity of strata arises a diversity of picture singularly delightful. It was a fine evening, when I made these observations; the sun was sunk toward the west, gilding the lake and the verges of the Innishowen range; the rays were shot almost horizontally between the sublime precipices and the fallen masses. Benyevenagh, with all his outline, seemed projected on the mellow sky. Ruined spires, fallen castles, with a thousand imaginary similitudes, surprised, delighted, and awed the contemplative mind. Before we close this investigation, (if I may presume upon any kindred curiosity,) it may be hoped that the reader would find that no ill-spent time, in which he follows me, in one or two excursions, to discover the materials, on which the great mountains of basalt are supported, through the interior of this most interesting district. Ascent of the Lyn-burn to the water-fall of Stradreagh. Under the bridge of Dirtagh, this stream crosses the Coleraine road; shortly after which, joining the Curley river, its banks discover the same strata of soft grit, as are already described. I propose to detail the ascent from this bridge upwards, as affording a very clear exposition of the strata, on which the basalt is ultimately incumbent. From the bridge of Dirtagh to the grazing park of Lisnagrib, is an ascent of about 100 feet perpendicular. Of this the entire is of red argillaceous grit, with cross-veins of a substance, in grain and consistence nearly similar, except that the colour is of a bluish grey. At the commencement of the park, the channel of the Lyn is a deep ravine; the successions of strata are exhibited in the following order: 1. After the commencement of the park, red soft grit, 4. Bluish clay, inclined to marle, 5. White lime, resting on a green marl-like substance, which does not effervesce, 6. Ochreous trapp, softer, as it is in contact with the limestone, occasionally resting on nodules of flint, one of which contains shells; the mass is confused with basalt, shapeless, tabular, and semicolumnar, over which is the water-fall. Feet. 20 1 75 5 6 50 Along the banks of this stream I found stalactites of lime, in porous masses; in other places, amianthus and mountain leather. The ascent of the Balteagh river is covered with rubble, until the level of the glebe. It begins here to discover the strata, over which it runs. The first is grit of a soft texture, and frequently endeavouring at a lamellated figure. It contains a considerable deal of calcareous matter, so much as to be valuable as a manure. We find it interspersed with fragments of quartz and hard shist, from the size of a grain of sand to that of a bean. Over the surfaces of the lamellated parts there is diffused a polish of mica, which gives it a distant resemblance to shistose mica. Observe that it is near to the strata of mica-shist. Higher up, on the bank below the church, a quarry of sandstone has been opened. It is excellent for building, though somewhat too much coloured by iron. The plane of the strata conforms to the general rule, rising to the south-west, in an angle of about seven degrees. The stones of this quarry separate into cubes, and parallelopipeds, with other figures, which approach to some of the shistose cristallisations; and, in fact, the bed of the river upward produces these substances, which may be called the connection between flag and freestone, until, at Mr. Boyle's green, tables of compact flag occur. This rests on a vein of quartz, four inches thick, and this again on shistose mica, which is in knotty and waving lines, and which contains specks of quartz and feld-spar. There is a continual succession of soft gritty strata, one placed over another, parallel to the plane of the limestone in Donald's hill. The quarry of Alknover, near Dungiven, is of the finest quality: the colour is bright tawney, not unlike that of the Portland stone. Many of our best buildings are from this quarry; but laying quite inland, and not convenient to the main road, its materials are not had without great expence. It is wrought into window-stools, quoinstones, grinding-stones, &c. at one shilling per cubic foot; it has been carried to Derry, to Down-hill, and even to Caledon. Examined, as a fossilist would desire, it would exhibit small crumbles of quartz, with sand of the same; the cement silicious. The strata rise to south-west; they are divided into irregular parallelopipeds, measuring, in general, ten feet by nine. The longest dimension of these rises to the south, the lesser dimension to the west. I believe, that the same stratified mass of grit is extended from the Balteagh' river, to that of Fahan-vale, Grestil, &c. The sandstone in these places would be valuable, only that its iron is in too great a quantity, and too much oxygenized, on which account the colour is that of a rusty red. I have mentioned this before. Under Sliabh-gallan, and above Moneymore, there is a quarry of reddish freestone. It is very like that of Fahan-vale; and I think it is connected with it. Iron. This is in great abundance throughout this county, either in an ochreous state, or mixed with manganese. It is nearly in a metallic state, in the lands belonging to the Cloth-workers, over Ballyhacket, where it caused the needle to vary and to dip, in a manner which at first surprised me, till I recollected the cause. Iron is found nearly in a metallic state also, in many of our basalt quarries: I have seen it in the softer stones employed for making roads, involucrated with folds of trapp, the interior nucleus being almost pure metal. In a mixed state, with manganese, called bog-ore or woad, it is abundant in the mountains near Glenrandle, and about Listress; and in the neighbourhood of our mountain streams, which issue from bogs, mounds of iron may be observed, in the character of yellow ochre. To the abundance of this metal, in the peat moss, is owing the red colour and weight of the ashes. Iron was formerly smelted in this county, at a place to this day called the Forge, on the site of which Mr. Henderson had a bleaching machinery, near Castle Dawson. The mine was in Sliabhgallan, and the person, who conducted the works at that time, was agent to the Drapers' company. The speculation was unsuccessful. - I have found excellent specimens of iron ore in Sliabh-gallan. Might it not be worked with success, by charring the mountain turf, which lies convenient to the mines? Copper and lead are found in this county, in small veins; but nothing worthy of mention has yet occurred. Gold. In Boat's Natural History of Ireland we find it reported, that “out of a certain rivulet in Nether Tyrone, (which is now that upper part of the county of L. Derry, subject to the ecclesiastical jurisdiction of the primacy) called Miola, the which, rising in the mountain Slewgallan, and passing by the village of Maghary (a mistake) falleth into the north-west corner of Lough-neagh, close to the place where the river Ban cometh out of it, a person had gathered one drachm of pure gold, concluding thereby, that in the aforesaid mountain rich gold mines do lie hid.” I have several specimens of quartz containing thin leaf of gold: these are found on the surface, and are, as I believe, adventitious. I do not think, that gold is found in basalt mountains, unless at the base, where the shist and quartz are the substrata. |