Haigh — Carboniferous Volcanoes of Philip stow n, King's Co. 29 



that which surrounds the hill. A small oval-shaped neck rises just south 

 of Barrysbrook House and close to the northern boundary of the ash, the 

 latter extending to the east, beyond the neck, in a tongue-shaped area, the 

 boundary of which is sharply marked off from the limestone plain by a low 

 but steep escarpment. The ash here shows signs of bedding which dips 

 parallel to the underlying limestone. The rock in this neck is a dark com- 

 pact basalt in which he numerous felspar laths in all positions in a matrix of 

 altered glass. Phenoerysts of augite with many smaller crystals are scattered 

 profusely through the rock (fig. 5). Much titaniferous magnetite occurs in 

 small grains, and a few long needles of apatite 

 are present. The glomeroporphyritie structure 

 is again a noticeable feature in the rock of this 

 neck. The olivine, as in the other specimens 

 described, is completely altered, while a fibrous 

 mineral occurs which seems to be an alteration 

 of the pyroxene, as a small patch of the original 

 mineral is seen in the centre. 



Near Gorteen, on the southern side of the 

 hill, and about two hundred yards south of the 

 cross-roads, another small outcrop of the intru- 

 sive rock is seen. It is only exposed in one 



place in an old quarry just north of a farmhouse near the road. It is a dark 

 crystalline rock, very hard and tough, and difficult to fracture. It is slightly 

 amygdaloidal, the cavities being lined with radial serpentine, and the interior 

 filled with caleite. Crystals of pinkish augite are common, and pseudomorphs 

 of olivine occur. Very little felspar is seen, and this only as microlites and 

 skeletons, whose species could not be determined. Much titaniferous mag- 

 netite is present in small grains. It was originally a rather basic type of 

 olivine dolerite, and, although much altered, has a specific gravity of 2 - 81. 



. In an old quarry in the Clonearl estate, about two miles south-west of 

 Croghan Hill, the igneous rock is seen overlying the limestone, which has an 

 easterly dip of 15°, the limestone occurring in thiek-and-thin-bedded shaly 

 bands. ~So ash was visible between the limestone and the basalt, nor was any 

 seen to overlie the basalt. On the Geological Survey map ash is shown to 

 the north-east as far as the bog ; but it is pointed out in the memoir that 

 " the ash marked on the map here is merely drawn on the supposition of the 

 ash at Boston extending south beneath the bog, as neither the ash nor any 

 other rocks are visible here." It is a dark fine-grained rock with a fair 

 vertical columnar structure, and . appears to occur as a sill which has been 

 intruded into the limestone. The latter does not appear to have been altered 



