CoLe—The Rhyolites of the County of Antrim ; with a Note on Bauzite. 95 
of the quarry already described, and the still more broken-down material of the 
braes themselves, are used for garden-paths in the neighbouring demesnes. ‘The 
braes above the quarry of fluidal rhyolite, and the Sandy Braes proper, north of 
the road from Doagh to Connor, are covered some four feet deep in rich yellow 
soil, which results from the decay of various rhyolites, with a trace of admixture 
from scattered erratics of basalt. Pebbles and boulders of glassy rhyolite are 
sifted out of this material by the cottagers, and are thrown in heaps beside the 
roads. The majority of these consist of black obsidian, commonly perlitic, and 
enclosing porphyritic crystals of quartz, orthoclase, and plagioclase. Some are 
so thoroughly traversed by perlitic structure as to appear pale grey, like the 
typical rocks described by Beudant, the perlites of the Glashiitte or Skleno valley. 
Others have bands of greenish lithoidal matter alternating with the glass, fluidal 
undulations being also exquisitely displayed; others contain coarse spherulitic 
ageregations, and have their hollows and cracks filled with massive opal, 
chalcedony, and agate.* A few are of the brown or black ‘ hornstone” type, in 
which the glass is almost masked by crystallisation; and these connect the 
obsidians with lithoidal rhyolites of the type common on the Carnearny braes. 
On traversing this moorland of Barnish, and the rough fields cut off from it, 
a number of small excavations are met with, and in almost all of them the same 
glassy rhyolites are seen. There is probably a square half-mile (a quarter of a 
square mile) of obsidian in this locality. In the floor of some of the little pits, 
this rock can be seen as a continuous mass; the quarrymen are only concerned 
in removing and sifting the rubbly material of the surface. In the upper four 
feet or so, the boulders of obsidian lie conspicuously in the yellow sand. In 
some cases this sand is derived from the decay of the glass itself, which 
becomes rusty-brown and very friable on its surfaces. The boulders are thus 
mere cores hitherto spared from decomposition. But at the west end of Sandy 
Braes there is an extensive section, in which the warm brown rubble surrounding 
the glassy boulders resembles a lithoidal rhyolite, and has a banded structure. 
Here the glassy surface-matter of a laya-flow has become broken up into blocks 
some 20cm. or more across, and has sunk into a lithoidal underlying layer, 
which has been more readily attacked by decomposition. 
Brecciation of the glassy products of rapid cooling, by movements going 
on in the still viscid layers below, is well known in connexion with modern 
lava-streams.t In parts of the floor of this shallow quarry, lithoidal rhyolite has 
been exposed, probably forming the main mass of the flow. It is a pink-red rock, 
resembling that about to be described from the east end of the Braes. Rhyolite 
* Compare Berger, op. cit., p. 190. 
+ Compare J. W. Judd, ‘‘ Contributions to the Study of Volcanos,” Geol. Mag., 1875, p.65. Also 
G. Cole, ‘‘ Devitrification of cracked and brecciated Obsidian,’’ Min, Mag., vol. ix. (1891), p. 272. 
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