98 Scientific Proceedings, Royal Dublin Society. 
slices the epidote is pale greenish-yellow, with only faint traces of 
dichroism: it is to this constituent that the rock, as a whole, 
chiefly owes its strikingly green colour. 
The ilmenite has undergone complete conversion into leucoxene, 
so that as a rule skeleton plates of leucoxene, often hexagonal in 
form, and penetrated by felspar, are all that remain to mark its ~ 
previous presence. 
The effects of pressure are seen in the occasional fracturing of 
the felspar and augite. 
The hummocks on the right-hand side of the road consist of a 
dark brownish-red felsitic-looking rock, with a platy or splintery 
fracture, in this and in its colour closely resembling some of the 
Cambrian slates of the district; indeed, in the case of the more 
thoroughly cleaved examples, some doubt may well be felt as to 
their true nature on first making their acquaintance in the field, a 
doubt that a glance through the microscope at a thin slice will 
immediately dispel. In places, spheroidal jointing is seen in the 
hummocks, the concentric planes of division being crossed by a 
second set of fissures running radially. Here and there minute 
vesicles and amygdaloids appear, and at one spot included frag- 
ments of calcite ; one of these, a rounded block of completely 
crystalline pinkish-red limestone, measures 6 inches in diameter, 
and is very unlike a segregation or concretionary product; it 
looks far more like a derived fragment, caught up by the ascending 
lava from some underlying stratum. The specific gravity ranges 
from 2°834 to 3:004; the mean obtained from six specimens is. 
291. 
The most coarsely crystallized example of these rocks I have 
met with happens to be somewhat vesicular, irregular cavities 
some half-an-inch in diameter, now filled in with calcite, occurring 
abundantly dispersed through it. In this, as in all the rocks on 
the right-hand side of the road, the chief mineral constituent is. 
felspar, which occurs in lath-shaped crystals, twinned once or 
twice, generally grouped, as many as six or eight together in 
stellate clusters. The ends of the crystals are frequently forked 
and the sides sometimes ragged; a thread of opaque white mate- 
rial, representing decomposed glass, usually runs through them 
axially. ‘The same opaque white material occurs between the 
crystals, and is sometimes distributed in groups of short parallel 
