Kinahan — On Granite and Metamorphic Rocks. 183 



matter, which was gradually being deposited as the water evaporated. In the associated 

 Leinster Type granite, especially to the southward, the composition of the "endogenous 

 veins" is more or less similar to that of the Aughowle pegmatyte. The exact limits of 

 the Aughowle pegmatyte are uncertain, the rocks being so much concealed by drift. 



The growan used to be largely sold in the city of Dublin, imder the name of " free- 

 stone," for domestic purposes. The disintegration of the Leinster Type granite, 

 especially that of the Co. Carlow, seems to be due in a great measure to the contained 

 quartz being made up of acicular particles ; but at the same time there must be some 

 peculiarity in the felspar that causes it also to decompose ; possibly the mica also may 

 have peculiarities. The disintegration of the Aughrim Type granite seems in a great 

 measure to be due to the quantity of marcasite in it, and to the white mica (mctrgaro- 

 dite ?). Growan is an excellent fertilizer on limestone soil, or on the tracts of limestone 

 drift. As pointed out by Haughton, most of the rich lands of the Co. Carlow are due 

 to the admixture of granite and limestone debris. 



The growan due to the disintegration of the Leinster Type granite ought to be useful 

 in the manufacture of china and coloured glass ; but it does not appear to have been 

 tested.] 



Devonian (?), Carboniferous, Trias (?), Eocene (?). Granites, 

 Elvans, Felstones, Eurytes, Whinstones. 



[The rocks in Croaghan, north of Philipstown, King's Co., are a protrude of 

 carboniferous age ; but the ages of the other later exotic rocks in the same district 

 are more or less open to conjecture. The granite of the Aughrim type may occur 

 as outliers in the schistose rocks, as it does near Auglrrim and Kathdrum, or in 

 different places as intrudes in the older granite (Leinster type). Under the latter cir- 

 cumstances, on account of the paucity of natural or artificial sections, it is difficult to 

 separate one variety from the other ; but J. Chaloner Smith, when reconstructing the 

 railway between Kingstown and Killiney, observed and pointed out two distinct classes 

 of rocks, one evidently of much later age than the other — the later rocks occurring as 

 intrudes partly in the old granite and partly in the mica schist. 



The exact age of this granite is uncertain. It may be Silurian, or Devonian, 

 of a similar age to the volcanic products so well represented in the provinces of 

 Munster, Connaught, and Ulster ; or it may be of the same age as the just men- 

 tioned Croaghan protrudes (Carboniferous), or even of that of the Mourne Moun- 

 tains granite (Triassic). There is no penological evidence by which its age can be 

 determined ; but lithologically it has affinity to the Mourne granite, being slightly 

 albitic — so it may possibly be of similar age (Triassic). 



The Aughrim type granite is an even, free-working stone, jointed in squarish 

 blocks, and having two "grains," along which it splits easily. It is very pyritous 

 (marcasite), and liable to disintegrate in concentric coats ; so that the outer parts of a 

 block may be much affected by weathering, and liable to peel off in spheroidal shells, 

 while the middle part of the block may be quite sound. A constant adjunct of the 

 intrudes is the " iron masking " of the neighbouring rocks. These seem to have been 

 impregnated with a solution that deposited marcasite, and this, by rapid decomposition, 

 has stained the rocks, which, from their appearance, are locally called "burnt rocks." 

 These burnt rocks, connected with the intrudes of the Aughrim type granite, are 

 similar to the "burnt rocks" containing the mineral channels of the Cos. "Wieklow 

 and Wexford, which formerly led me (volume v., p. 304) to suggest that the 



