KiNAHAN — Eurites, or Basic Felstones of Silurian Age. 339 



From the latter area two specimens are exhibited ; both show the 

 gradual merging of the rock into elvan, as they contain free quartz. 

 This, however, might be expected, as one of the specimens is from the 

 intrusive mass, while the other is from the vicinity of it. 



That from Lough Guitaue, near Eallarney, is a specimen of a 

 dark-green feldspathic rock ; it has a specific gravity of 2-63, The 

 macroscopic examination of it shows it to consist of a finely granular 

 ground-mass or matrix, scattered through which are small crystals of 

 feldspar, some of which appear to be orthoclase, while others are 

 triclinic ; some have striae on the basal section, some are of an opaque 

 white, with bluish tinge ; there are also crystals and blebs of quartz. 

 On looking through a thin section of this rock, a structure appears in. 

 the ground-mass which might be described as a banding, being a 

 series of alternate semi-opaque and more pellucid parallel bands. The 

 feldspar is cloudy, the quartz clear. 



Microscopically , the ground-mass of this rock consists of a crypto- 

 crystalline base, with numerous crystallites of feldspar (both ortho- 

 clase and triclinic) quartz, small fragments apparently of hornblende ; 

 in some places long acicular crystallites or crystalloids, sometimes 

 grouped radially, which are clear and pellucid. A chloritic mineral 

 (viridite), and a dusty-looking opaque granular mineral (opacite) occur 

 plentifully, ferrite sparingly. In a few places aggregate polarization 

 occurs, consisting of a clear, circular portion with a dark cross, 

 which rotates on rotating the polarizer, but remains stationary on 

 rotating the slide. The banding noticed in the macroscopical exami- 

 nation seems, with polarized light and under a power of one hundred 

 diameters, to be due to a difference in the degree of crystallization, 

 the more largely crystalline bands being the more pellucid. In this 

 ground-mass are developed the macroscopical crystals of feldspar and 

 quartz. The feldspars, as already mentioned, are both orthoclase and 

 triclinic ; some of them being very peculiar, showing a remai'kable 

 banding or interlamination under polarized light. Under ordinary 

 light they appear rather clouded, from containing opacite ; some of 

 them are imperfect, and seem to have been broken subsequently to 

 their formation, some of the ground-mass having evidently intruded 

 between the fractured portions. The bright little specks occurring in 

 these feldspars under polarized light are found, when examined 

 under a higher power (300 diameters), to be little iridescent 

 patches, and are probably thin films of calcite. On applying hydro- 

 chloric acid to the specimen, a slight effervescence takes place, about 

 and along certain Hues in the feldspars, and at little specks through 

 the ground-mass, indicating, probably, films and specks of calcite. 

 Large quartz crystals are not well represented in the slide ; generally 

 the quartz is in small, rounded patches, though in some cases in well- 

 crystallized forms ; all are clear. Some of the larger pieces contain 

 stone enclosures. 



The specimen from Binaunmore, Co. Kerry, is that of a compact, 

 olive-green rock, having a specific gravity of 2'63. The ground- 



