Basalt next claims our attention, in this necessarily im perfect account of the mineralogy of Ireland. " The ba saltic district of this country occupies a range of coast stretched out from the estuary of Carrickfergus on the one hand, to Lough Foyle on the other, and extends inland to the southern shores of Lough Neagh." The basaltes of this district is generally amosphous, but not unfrequeetly disposed in thick hells. At the Giant's Causeway it is most perfect in its for m. Here, there are large pillars of it perpendicular to the horizon ; in other places, Meir po sition is oblique ; and in a few, the basaltic pillars form a variety of regular curves. At the Donn Point, in the island of Raghery, all the three kinds are seen, the pillars being perpendicular, horizontal, and bending. (S-e GIANT'S CAUSEWAY.) The promontories of Fairhead, aad Bengore, (see FAIRHEAD,) and Cape Pleskin, have already been mentioned, in describing the coast of Ireland , but it will be proper in this place, again to advert to the last in a geological point of view. About ten or twelve feet from the soil Cape Pleskin " begins to assume a columnar ten dency, forming a range of mass) pillars of basaltes, which stand perpendicular to the horizon, presenting, in tilt_ sia:rp face of the promontory, the appearance of a rwgnifi..erit gallery or colonnade upwards of sixty feet in height This colonnade is supported on a solid base of coarse black ir regular rock, near sixty feet thick, abounding in blebs and air-holes ; but though comparatively irregular, it may be evidently observed to affect a peculiar fissure, tending, in many places, to run into regular forms, resembling the shooting of salts, and many other substances, during a crystallization. Under this great bed of stone stands a a second range of pillars between forty and fifty feet in height, less gross, and more sharply defined than those of the upper story ; many of them, of a close vein, emulating even the neatness of the columns in the Giant's Causeway. This lower range is borne on a layer of red ochre stone." The ranges of pillars are more perfect in proportion as they lie deeper in the ground. The second range of Cape Pleskin consists of pillars more perfect than the upper range, and the basalt itself has fewer irregularities and im perfections ; and the pillars of the Giant's Causeway, which lie still lower, are yet more perfect, as well as the basalt more close and uniform in its texture. Where the forms of crystallization of the basalt are imperfect, the pil lars assume various directions ; but their general and na tural position appears to be horizontal. The following is a list of the strata at Cape Plcskin, as given by Mr Hamilton in his Leiters on this coast.
draining the bogs of Ireland, (to which we have been indebted,) enable us to ado to the sketch just given, ol the gt ',logy and miner alogy of some parts of this country, a f.•.% particulars on these subjects. At the northern edge ol t island of Allan, which adj the bug el that name, st. titled limestone makes at the surface, at ah .1 gle of 5°, and with a dip 20° east of south. Between tl.is edge and the base of the Hill of Allan, hills of lime stone gravel oct ; but at the base a rock appears, com post d uf breccia ; thin beds ol a deep brick red slate ; clay much interspersed with mica, is found liter stratified pith the breccia. To the south rises the Hill ol Allan. compos ed of an iiregolar unstratilied mass of fine grained green stone, the crystals of hornblende and feldspar being very minute. Near the summit, the ro.k becomes more cry's Ditached masses of beautiful porphyrctic green stone, thickly studdc d with large crystals of felspar, are fee quentiv met on the surlace. A hill to the south-west of the Hill of Allan, is also composed of greenstone.
fire information regarding the strata of part of the Bog of Allan, (and it is highly probable, that the other bogs of Ireland are similarly constituted,) which is contained in the fir st report of the commissioners, we shall give in the words ol that report.
" It appears from Mr. Griffith, (the gentleman employ ed to survey this district,) that each of the four bog:, inclu ded in the subject of his report, is a mass of the peculiar substance called peat, of the average thicket ss of 25 feet, nowhere less than 12, nor found to exceed 42 ; this sub stance varying materially in its appearance arid properties, in proportion to the depth at which it lies. On the upper surface, covered with moss of various species, and to the depth of about 10 feet, composed of a mass of the fibres of similar vegetables in different stages of decomposition, pro portioned to their depth from the surface,—generally, how ever too open in their texture, to be applied to the purposes of fuel. Below this lies generally a ligh blackish brown turf, containing the fibres of a moss still visible, though not perfect, and extending to a further depth of perhaps 10 feet under this. In the instance exhibited in the section at the close of Mr. Griffith's report are found small branches and twigs of alder and birch ; but we do not understand him as being of opinion, that such is by any means gene rally the case. At a greater depth, the fibres of vegeta ble matter cease to be visible ; the colour of the turf be comes blacker, and its substance much more compact, its properties as fuel more valuable, and gradually increasing in the degree of blackness and compactness proportionate to its depth. Near the bottom of the bog it forms a black mass, which, when dry, has a strong resemblance to pitch, or bituminous coal, and having a conchoidal fracture in direction, with a black shining lustre, and suscepti ble ol receiving a considerable polish. Immediately below this lower stratum, there is generally found a thin stratum of yellow or blue clay, varying in thickness from one to six feet. In some places, the peat rests un a thinner stratum of yellowish white marl, containing on an average about 60 per cent. of calcareous matter. This stratum of clay in this district, universally rests on a solid mass of clay and limestone gravel mixed together, and extending to an un known depth." Recent researches have discovered some rare minerals in Ireland, which it will be proper briefly to notice here. Vesuvian has been found at Kilranelah, in a rock compos ed of common garnet, quartz, and feldspar. The crystal line form of the vesuvian, however, is not well exhibited. Grenatite occurs, in a micaceous compound, in the lead mines in the county of Wicklow. The precious beryl has been found imbedded in granite near Lough Bray ; and cronebane in the same county, and in the Dubith inumitains near Dundrum. The Dunce mountain, in the county of Wicklow, is composed of micaceous slate, in which anda lusite has been found. A variety or the same mineral has been found in great abundance at Keiliney, in the county of Dublin. Tne andalusite ol Douce mountain, is accom panied by a crystallized mineral, the characters of which have much affinity to those of indurated talc, the occurrence ol which in crystals has hitherto been very rare. Very distinct specimens ol hollow spar have been found at and near Baltinglass, in the county of Wicklow. Pitch stone, traversing granite, has been found ,tear N..wry, in the coun• ty of Down The granular sulphate of barytes, accompa nied by iron pyrites, has been found on the sea shore near Clonakilty ; and Wavellite, very similar in its external characters and analysis to the Waveilne of Devonshire, as described by Sir H. Davy, has been found about ten miles south east from the city of Cork. Near the extremity of the granite district in Kilkenny, jaspers of various sizes have been discovered, a fow feet below the surface, in yeliow clay. The county ol Kerry is remarkable for transparent regular crystals, known under the name of Kerry stories. They are harder, larger, and possess more brilliancy, than the Bristol stones. Amethysts have been discovered in the clefts near Kcrryhead.