274 Dr. FiTTON on the Geology of the 



eastky 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^ l^c. 



I. Vesuvian. — (Idocrase^ Haiiy). This substance was observed 

 by Mr. Stephens in specimens found by me at Kilranelagh, where 

 it occurs in irregular crystalline masses, in a rock composed of 

 common garnet of a reddish-brown colour, 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 Vesuvian is not well exhibited, although 

 some indistinct prisms are to be observed. In general, its particles 

 assume a scapiform aggregation, sometimes approaching to stellular, 

 a form which I have not observed in specimens of this substance 

 from other places ; but its fusibility, lustre, [colour, and other cha- 

 racters leave no doubt as to its nature. 



The blocks of this compound at Kilranelagh were not in their 

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

 render it probable that they were not far removed from it. Garnet 

 rock is described as occurring in beds in primitive mountains, and 

 the country at Kilranelagh is of that description. 



It is remarkable, that a compound much resembling that which I 

 have described, occurs also in the County of Donegal, from whence 

 specimens now in the cabinet of the Dublin Society, and that of 

 Dublin College (No. 30.), were obtained. The garnet and vesuvian 

 in these specimens, are scarcely to be distinguished from those of 



