Vol. 5 2. J ON THE KILDARE INLIER. 601 



ments include both rounded and angular individuals, and are of all 

 lengths up to about a foot. This irregular base to the coarse rock 

 was also noticeable to some extent on Grange Hill. 



The coarse rock occurs along two parallel lines on the south-eastern 

 face of the hill, the lower line ending off abruptly about 30 feet 

 below the point where the upper line as abruptly begins. There 

 seems to be a small fault here causing this discontinuity. Exposures 

 of the coarse rock also occur at various points on the western face 

 of the hill, and one small exposure was found low down the hill- 

 side, due east of the Cariick tower. 



The appearance of this rock in the field is exactly like that of the 

 coarse basalt from Grange Hill. There is the same grey, somewhat 

 crystalline groundmass enclosing the same large white or greenish- 

 white porphyritic felspars, which are often almost circular in outline 

 and of no great thickness, while most of them lie with their flat faces 

 parallel to each other. Vesicles filled with calcite and a chloritic 

 mineral are similarly to be observed in the rocks from both hills. 



Under the microscope the resemblance between the coarse rocks 

 of the two hills holds equally well (see PI. XXVIII. fig. 2). In 

 each we see the same prominent groundmass formed of small 

 idiomorphic crystals of plagioclase and allotriomorphic granules 

 of augite in almost equal proportions, the same development of 

 magnetite, green serpentine, and yellowish pseudomorphs after a 

 rhombic pyroxene, while the porphyritic constituents in the two 

 cases are seen to be fresh augites and large felspars allied to 

 labradorite. 



Most of the upper part of the hill is formed of an andesitic rock 

 [67, 78], which overlies the coarse basalt and has a very definite 

 character. It is rather light green in colour and marked with 

 numerous red spots which are patches of haematite. A hand- 

 specimen shows no obvious porphyritic felspars, but many fresh 

 black augites are to be seen. 



Under the microscope (see PI. XXVIII. fig. 6) it is seen to be 

 characterized by having a groundmass crowded with small rect- 

 angular or nearly square sections of a fairly fresh felspar allied to 

 oligoclase ; but it contains also augite, bastite-pseudomorphs after 

 a rhombic pyroxene, and magnetite. Porphyritic felspars occur, 

 much altered and epidotized, but possessing an outer rim of fresh 

 secondary felspar. Porphyritic augite and altered rhombic pyroxene 

 are to be seen, the two minerals being sometimes intergrown in a 

 complicated manner (see PI. XXVIII. fig. 3). It is the occurrence 

 of abundant small felspars which appear square or rectangular in 

 section that marks off this hypersthene- or enstatite-augite-andcsite 

 from the other rocks of the hill. An analysis of this rock showed 

 58*5 per cent, of silica, while the specific gravity was 2*81. 



The rest of the north-western slope of the hill is formed of rocks 

 dark in colour, which show very obvious porphyritic felspars in a 

 hand-specimen. They almost invariably show bastite-pseudomorphs 

 after rhombic pyroxene, augite, and magnetite in their groundmass, 

 together with felspars having low extinction-angles, while the 



