112 Cotr—The Rhyolites of the County of Antrim ; with a Note on Bauvite. 
neck of Sliemish towering in the distance, the eye is caught by a strange white 
boss in the midst of the bog, utterly at variance with its surroundings. Its form 
reminds one of the ‘‘ quartz-knobs” of some metamorphosed areas. ‘This little 
protrusion is composed of the most beautifully fluidal rhyolite, the flow-planes 
being again vertical and running right across the boss. The whole mass is so 
small that it might possibly be a displaced portion of a lava-stream ; as it stands, we 
must regard it as representing a volcanic neck. The geological surveyors* report 
aptly that the laminze in the field ‘‘remind one of the structure of slate or shale.” 
This delicately banded and fluidal lava is here grey, here pinkish, here faintly 
yellow brown. In part it has been brecciated, or has picked up dull grey angular 
fragments of another rhyolite. The flow-bands, visible with the naked eye, are 
often alternately pink-brown and pale-grey, and fifty may occur within a centi- 
metre. Here and there a few vesicles occur, greatly flattened out between two 
adjacent bands; in some of these, crusts of hyalite have arisen. 
Some of the bands are seen to consist of small spherulites, and minute granules 
of quartz glisten throughout the mass. The only porphyritic crystals observed 
are rare flakes of biotite, one of which is 5 mm. across. 
The specific gravity of this rock varies more than might be expected, and it is 
probably more glassy in some layers than in others. The results obtained from 
various specimens range from 2°40 to 2°49. 
Mr. A. Percy Hoskins, F.I.C., F.C.S., of Belfast has very kindly made a 
quantitative analysis of one of the compactest specimens. The work was done 
under considerable disadvantages, including the proximity of building-operations ; 
but Mr. Hoskins informs me that the excess in the analysis is likely to ihe mainly 
in the lime. The important results for the silica, the joint alumina and iron 
oxide, and the alkalies, have been satisfactorily checked. 
BanpEeD RuyoLirE of CLouGHWATER, Co. AN?TRIM. 
Analysis by A. P. Hoskins, P.I.C., FCS. 
SiliGares, Ge Newer on ee eee ORO, 
Alumina 2.22) .2. sev peep LOseo 
Ferric Oxide . .. . 2°04 
(aime Me te cat eee eee 
Magnesia. 8 Oe 
Potashis 2 es cee as POR 
Sodan MM eee JR S6 
Loss on ignition . . . 0°97 
102°51 
* Mem. toSheet 20, p. 1]. 
