92 Scientific Proceedings, Royal Dublin Society. 
presents a corroded appearance. Small octahedra, grains, and 
plates of magnetite are abundantly scattered amongst the other 
er 
<= 
a 
—- 
sw: 
| 
Fie. 2.—Augite Andesite—The Pyroxene is indicated by close parallel fine lines, the 
Felspar is left white, the Magnetite, cross-hatched, and the Glass dotted (x 225). 
constituents. The colourless glass is rendered brown by included 
globulites, and sometimes contains black belonites. 
Phenocrysts of plagioclase felspar, 
fragmentary and often highly corroded, 
lie scattered here and there. One finely 
twinned example gave a symmetrical ex- 
tinction of 10°, and is probably therefore. 
oligoclase. A curious fringe sometimes 
extends from the margin of the pheno- 
eryst inwards.. This marks the advanc- 
ing invasion of the felspar by the glassy 
Fic. 3.—-Felspar invaded by the ; 
glassy base (x 187). mesostasis; each fibre of the fringe con- 
sists of a row of minute granules, resembling globulites (fig. 3). 
