Yol. 52.] ON THE KILDAEE 1NLIER. 597 



formed of small crystals of oligoclase exhibiting excellent flow-struc- 

 ture, and embedded amongst them occur large porphyritic felspars, 

 now entirely replaced by calcite and chlorite. The vesicles are tilled 

 with a chloritic mineral and quartz, the quartz often showing a 

 partially spherulitic structure. Such an andesite occurs also in a 

 similar position with regard to the ash-bed at the north-easternmost 

 exposure on the hillside. Sections of the ash itself (see PI. XXVIII. 

 rig. 4) show more or less rounded fragments of lava in which small 

 felspar-needles are easily recognizable, and these fragments, together 

 with numerous broken felspars, are embedded in a matrix of calcite 

 and of isotropic brown material. Quartz-grains and patches of a 

 green chloritic mineral are also present. The most interesting 

 exposure of this rock is close to Grange Hill House Cottage, where 

 it becomes more gritty, the quartz-grains increasing in number 

 while the fragments of lava and shattered felspar-crystals are not 

 nearly so evident ; and here, as mentioned above, it becomes very 

 fossiliferous. 



Above the ash-bed there is seen in places another band of ande- 

 site, also light green in colour, and sometimes very vesicular (see 

 PL XXVIII. fig. 5). A section shows a fresh and abundant 

 groundmass composed of acicular plagioclase-felspars exhibiting 

 flow-structure, granular augite largely replaced by calcite, and 

 much magnetite. One slide also shows some bastite-pseudomorphs 

 after a rhombic pyroxene. The porphyritic constituents are large 

 felspars, often completely replaced by calcite, while the vesicles are 

 filled with an outer ring of quartz and an inner mass of a chloritic 

 mineral, which is often of a slaty-blue colour in polarized light. 



This andesitic flow is covered by a basalt, sometimes dark and 

 compact, sometimes very vesicular. Exposures of this basalt are 

 fairly frequent along the hillside, the rock being recognized by its 

 very fresh black porphyritic augites, sometimes | inch long ; occa- 

 sionally, however, green platy felspars are the more obvious 

 porphyritic constituents. One of these rocks was found to have a 

 specific gravity of 2*93, and a silica-percentage of 48*15. Some 

 specimens show a red mineral with a good cleavage, occurring as 

 small spots throughout the rock. Under the microscope the ground- 

 mass of this rock is seen to consist chiefly of lath-shaped felspars 

 and grains of augite with a certain amount of interstitial matter. 

 The porphyritic augites are, as a rule, well preserved; they some- 

 times show a zonal structure, and often occur in groups of irregular 

 crystals ; in one instance excellent ' hourglass structure' was clearly 

 seen. The porphyritic felspars are seldom very fresh, though there 

 is often a kernel of much altered material surrounded by a marginal 

 deposit of fresh secondary felspar. 



The red mineral which has been mentioned above as being visible 

 as spots in a hand-specimen appears to be an iron oxide, generally 

 replacing augite (see PI. XXVIII. fig. 1). In some cases it occurs 

 as a more or less circular core within a mass of secondary material 

 which fills up completely the space originally occupied by the augite. 

 Sometimes, however, the iron ore is associated directly with augite, 



