28U 



IRELAND, 



StoiiMic*. beneath the basalt mountain of Sleeve-Gallen in the 

 """V^ county of Derry. It is every where used for architec- 

 tural purposes. 



The following facU respecting the granite near Dub- 

 lin, may be interesting in a geological point of view. 

 From the shore, on the south side of Dublin Bay, there 

 passes, in a south- western direction, a broad body of 

 granite, bounded on its eastern and western sides by 

 incumbent rocks of great variety. At Killarney, schis- 

 tose rocks repose for a considerable extent on granite ; 

 and the line of junction, which begins at the sea side, 

 may be traced for some miles across the country. On 

 the shore, it is traversed by numerous veins, many of 

 which are themselves composed of granite ; and, in 

 some instances, two veins of this substance, differing 

 from each other, and from the mass, in fineness, and in 

 the proportion of their jngredients, are seen to inter- 

 sect. The actual contact of granite with incumbent 

 rocks, has been observed at saveral places in the coun- 

 ties of Dublin and Wicklow. On the shore of Dub- 

 lin Bay, not far from Blackrock, a mass of compact 

 limestone is visible within a few fathoms of the gra- 

 nite ; but, in the intermediate space, the rock is con- 

 cealed. On the western boundary of the granite 

 rocks nearest to Dublin, rocks composed of trap occur; 

 and thence, to the south-west, along the borders of the 

 counties of Wicklow and Kildare, there are various in- 

 termediate rocks between the granite and the limestone 

 of the flat country to the westward. 



Liinestor e. Limestone is met with in general in great abundance 

 in all the counties of Ireland, except Wexford, Wick- 

 low, Tyrone, and Antrim. It has already been men- 

 tioned, in treating of the soils of Ireland, that the ri- 

 vers Barrow, Lee, Bride, Kenmare, and Blackwater, 

 form the boundary of the limestone districts in their re- 

 spective courses. Of this mineral, there are several 

 kinds, both such as are interesting to the geologist, and 

 such as are useful in an economical point of view. The 

 quarries in the immediate vicinity of Dublin, afford 

 many varieties of calcareous productions. The caelp of 

 Mr. Kirwan is the prevailing rock. Brown spar is 

 found in some quarries ; and beds of magnesian lime- 

 stone have been observed on the Dodder. The lime- 

 stones of Ireland are not less important in an economi- 

 cal point of view. Limestone of a fine white grain, ly- 

 ing in strata from four inches to two feet thick, and of 

 which columns have been raised between nine and ten 

 feet long, and from fifteen to eighteen inches in diameter, 

 abounds at Ardbraccan, in Meath. This limestone re- 

 ceives a very high polish ; and, when long exposed to the 

 air, assumes a greyish colour. Blue and white limestone 

 found in the county of Derry. Some of the former is 

 little inferior to marble. But perhaps the most useful 

 limestone for building is that found in Kilkenny. It is 

 of various colours, white, reddish, and black. The last 

 is of a remarkably fine texture, and susceptible of a high 

 polish. All the limestone of Kilkenny contains marine 

 shells of various species, as well as impressions of coral- 

 eries, &c. Marble, by no means of inferior quality, 

 i met with in many parts of Ireland. The most beau- 

 tiful is that of Kilkenny. Tin Black Quarry, which 

 lies about half a mile to the south of the town of Kil- 

 kenny, affords a species of marble nearly equal in qua- 

 lity to that of Italy. The ground is black, varied with 

 white marks, which assume a stronger tint when expo- 

 sed to the air. About 50 tons annually are exported. 

 Marble is also found in the counties of Cork, Armagh, 

 Down, Kerry, &c. Limestone, containing iron and 

 manganese, is found in various parts of Kilkenny. A 



species of whetstone, which, after being boiled in oil, is Statistic 

 used by the country people for whetting razors, &c. is S """V^ 

 met with on the mountain of Mangertan, The moun- 

 tain of Altahoney, in county Dowq, abounds in white 

 calcareous spar, which is used for tombstones, window- 

 stools, &c. In the Cave of Dunmore, in the county of 

 Kilkenny, alabaster abounds in large masses. 



Basalt next claims our attention, in this necessarily Basalt. 

 imperfect account of the mineralogy of Ireland. " The 

 basaltic 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 unfrequently disposed in thick beds.' At the Giant's Giant's 

 Causeway, it is most perfect in its form. Here, there Causewaj 

 are large pillars of it perpendicular to the horizon ; in 

 other places, thejr position is oblique ; and in a few, 

 the basaltic pillars form a variety of regular curves. 

 At the Doon Point, in the island of Raghery, all the 

 three kinds are seen, the pillars being perpendicular, 

 horizontal, and bending. (See GIANT'S CAUSEWAY.) The 

 promontories of Fairhead, andBengore, (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 tenden- 

 cy, forming a range of massy pillars of basaltes, which 

 stand perpendicular to the horizon, presenting, in the 

 sharp face of the promontory, the appearance of a mag- 

 nificent gallery or colonnade upwards of sixty feet in 

 height. This colonnade is supported on a solid base of 

 coarse black irregular rock, near sixty feet thick, abound- 

 ing in blebs and air-holes; but though comparatively 

 irregular, it may be evidently observed to affect a pecu- 

 liar fissure, tending, in many places, to run into regu. 

 lar forms, resembling the shooting of salts, and many 

 other substances, during a hasty crystallization. Under 

 this great bed of stone, stands 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 imperfections ; and the pillars, of the Giant's Cause- 

 way, 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 im- 

 perfect, the pillars assume various directions ; but their 

 general and natural position appears to be horizontal. 

 The following is a list of the strata at Cape .Pleskin, Strata 

 as given by Mr. Hamilton on his Letters on this coast, fiere. 



No. 1. Summit, irregular basaltes, shivered and 



cracked at the surface, 12 feet. 



2. Perpendicular range of gross pillars, con- 

 taining air-holes, 60 feet. 



3. Gross bed of rude basaltes, shewing 

 marks of a tendency towards forms, re- 

 sembling an imperfect crystallization, 60 feet. 



4. Second range of regular pillars, neat, 



and divided into joints, .... 40 feet. 



Carry over 



172 feet. 



