Cotr— The Rhyolites of the County of Antrim; with a Note on Bauxite. 115 
The rock is thus a close ally of that of Tardree, analysed by Mr. Player, and 
differs mainly in having a somewhat higher proportion of soda. 
Two types of this rhyolite have been examined microscopically. One shows 
bands made up of minute brownish spherulites, through which the flow-structure 
runs; while, alternating with them, are broader bands in which the spherulites 
are not so clearly arranged, but lie scattered in a more dusky glass crowded with 
globulites. With a high power, a delicate radial structure can be seen in the 
spherulites. Among the microlites and crystallites, there are crowds of red rods, 
occasionally forming geniculated crystals, like the minute rutiles of Sandy Braes. 
Such quartz crystals as can be identified occur in the more dusky bands, and one 
‘25 mm. long is quite a giant among them. 
The second specimen is still more delicately banded (PI. IV., fig. 6), and 
includes some dull elongated flakes of another kind of rhyolite. Quartz, and not 
tridymite, seems to have crystallised out along the hollows. The whole rock shows 
minute radial spherulites under a high power, and rods of rutile occur everywhere, 
lying for the most part parallel to the delicate flow-structure. They are thus, as 
at Sandy Braes, connected with the primary processes of crystallisation in the rock. 
Biotite is the only recognisable ferromagnesian constituent, and occurs 
minutely in the spherulitic ground, with granules of quartz and flakes of felspar. 
But, as a whole, the rock is composed of crystallites, not crystals, and it is this 
extreme delicacy of structure which has enabled it to show the phenomena of flow 
so perfectly. 
The parallelism of the flow-planes across the exposed boss in the middle of 
the bog may indicate that the vent was in this case a short vertical fissure. It 
would be well to watch the progress of excavations in the adjoining peat, on the 
chance of some junction of rhyolite and basalt being eventually revealed. 
TX.—Conc.vsion. 
In concluding this detailed examination of the rhyolites of the county of 
Antrim, I may perhaps be allowed to say how attractive this quest has been for 
me, ever since Mr. W. J. Knowles of Ballymena sent a fragment of perlite from 
Sandy Braes to Prof. Judd’s laboratory some fifteen years ago. In 1891 I first 
crossed the Tardree area, inspired by the fine series of specimens collected by Mr. 
M‘Henry for the Geological Survey. In 1892, Mr. G. W. Butler and myself 
visited Hungary, in order to become acquainted with the rhyolites of a classical 
area on a bold and open scale. This journey only rendered more apparent the 
variety and beauty of the products of the voleano of Tardree. In the foregoing 
paper I have endeavoured to make some contribution towards our knowledge 
of them. Observations in the field, aided by the lens, have been of primary 
importance; in the laboratory, the tridimensional methods of the older workers 
TRANS. ROY. DUB. SOC., N.S. VOL. VI., PART Ill. S) 
