County Armagh Geology

The geological features of the county are various and interesting. The mountain of Slieve Gullion, in its south-eastern extremity, is an offset of the granite district of Down, and is remarkable for the varieties of which it is composed. It is in the form of a truncated cone, and presents on some sides mural precipices several hundred feet in height, from which it acquires an appearance of greater elevation than it really attains: the summit is flat, and on it is a lake of considerable extent. The granite of this mountain, particularly that procured near the summit, is frequently used for millstones, being extremely hard and fine-grained, and composed of quartz, feldspar, mica, and hornblende. This, indeed, is here the common composition of this primitive rock, the feldspar being grey and the mica black. Sometimes the hornblende is absent, in which case the rock is found to be a pure granite; and at others it graduates into a beautiful sienite composed of flesh-coloured feldspar and hornblende. Flesh-coloured veins of quartz are also found to variegate the granite, in a beautiful manner, in several places.

On the south, towards Jonesborough, the sienite succeeds to the granite, and afterwards passes into porphyry, which is succeeded by silicious slate. The Newry mountains and the Fathom hills are composed of granite. Around Camlough mica slate is found in vast beds. Westward the granite district of Slieve Gullion extends to the hill above Larkin-mill. on the western declivity of which the granite basis is covered by almost vertical strata, composed first of an aggregation of quartz and mica with steatite, which in the distance of about a quarter of a mile is occasionally interstratified with greenish grey clay-slate, of which the strata still further west are wholly composed. Several slate quarries have here been opened and partially worked, but none with spirit or skill: the principal are at Dorcy, Newtown-Hamilton, Cregan-Duff, and in the vicinity of Crossmeglan. Further distant this becomes grauwacke slate, by being interstratified with grauwacke. In the neighbourhood of Market-hill the strata comprise also hornblende slate and greenstone porphyry.

Sandstone is also connected with this district; there is a quarry of remarkably fine freestone at Grange; and on the surface of the southern confines is seen the intermixture of grit and limestone rocks above noticed. Trap rocks, forming a hard stone varying in hue between dark green and blue, here called whin, are found in various places in huge blocks and boulders, or long narrow stones. The substratum of the eastern portion of the county varies between a silicious schistus and an argillaceous deposit, forming a grauwacke district, which extends across to the western confines of the county. The west and middle of the county is limestone, which is generally white, except in the vicinity of the city of Armagh, where it assumes a red tinge, exhibiting that colour more distinctly as it approaches the town, improving also in quality, and increasing in the varieties of its shades.

The minerals, as connected with metallurgy, are so few as scarcely to deserve notice, lead only excepted, a mine of which was worked in the vicinity of Keady, on a property held by the Earl of Farnham, under Dublin College; but after much expenditure the operations were discontinued in consequence of the loss incurred, which, however, has been attributed to the want of skilful or honest superintendence. Lead ore has also been found near Market-hill, in several places near Newtown-Hamilton, on the demesne of Ballymoyer, near Hockley, in Slieve Cross, near Forkhill, and in the parish of Middleton. Some indications of iron, imperfect lead, regulus of manganese, and antimony, have been, found in a few spots. The other mineral substances found here are potters' clay and a variety of ochres. Various kinds of timber, particularly oak, pine, and yew, have been raised out of the bogs; petrified wood is found on the shores of Lough Neagh; and fern, spleenwort, and mosses have been discovered in the heart of slaty stones.