«S4 



MounJains 



Vesuvian. 



GEO LOGY OF THE VICINITY OF PUBLIN. 



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Of the mountains nearest to Dublin, one of the highest, 

 Garrycastle, is 1531.7 feet above the level of the road at 

 Ballinteer; and the Three Rock mountain is 1247.9 feet 

 above the same place, the elevation of which is considerable. 

 The highest point of Howth is 567 feet above high-water 

 mark. 



Account of Minerals, Sfc, 



1. Vesuvian. — /' Tdocrase, H&ny). This substance was 

 observed by Mr. Stephens in specimens found by me at Kil- 

 ranelagh, where it occurs in irregular crystalline masses, in 

 a rock composed of common garnet of a reddish-brown co- 

 lour, of quartz for the most part greenish, apparently from 

 the admixture of a lamellar fossil of that colour, and a small 

 quantity of felspar. The crystalline form of the garnet is 

 here often very distinct, but in the specimens hitherto found, 

 that of the V esuvian is not well exhibited, although some 

 indistinct prisms are to be observed. In general, its parti- 

 cles assume a scapiform aggregation, sometimes approach- 

 ing to stellular, a form which I have not observed in speci- 

 mens of this substance from other places ; but its fusibility, 

 lustre, colour, and other characters leave no doubt as to its 

 Mature. 



The blocks of this compound at Kilranelagh were not in 

 their natural place, but their size, their great weight and 

 shigulai- form render it probable, that they were not far re- 

 moved from it. Garnet rock is described as occurring in 

 beds in primitive mountains, and the country at Kilrane* 

 lagh is of this description. 



ft is remarkable, that a compound much resembling that 

 which I have described occurs also in the county of Done- 

 gal, whence specimens now in the cabinet of the Dub- 

 lin Society, and that of Dublin College, No. 30, were ob- 

 tained. The garnet and vesuvian in these specimens arer 

 scarcely to be distVnguished from those of Kilranelagh ; and, 

 a£ at that place, are accompanied by quart?, often of a simi- 



above the level of the cross roads at the bridge of Tuckmill, a little vil- 

 lage on the river Slaney ; the elevation of which above the sea will be 

 yery well supplied when the line of the grand canal shall be extended im 

 this direction, as is no>»r intended. 



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