CoLte—The Rhyolites of the County of Antrim ; with a Note on Bauxite. 105 
The traditional and continuous dome of ‘“ trachyte-porphyry” appears in 
force in the longitudinal section of the Geological Survey, sheet 31, published 
in 1891. It is represented as traversed by basalt dykes, some of which must be 
regarded as expressions of opinion. ‘There is, it is true, an odd little exposure 
of crumbling and spheroidal basalt, south of the Doagh road, opposite the 
western quarries of Sandy Braes. This is probably, from its steeply inclined 
contact-plane with decomposing rhyolite, a dyke belonging to the upper basaltic 
series. 
To conclude, then, Professor Hull, who regarded the Tardree massif as a 
voleano,* seems to have insisted too little on its complexity, too much upon 
relationships which are confessedly dubious in the field. Sir A. Geikie was 
inclined to press too far the analogy with the intrusive ‘“‘ granophyres” of Mull 
and Skye. On the moorlands themselves, the evidence points to the occurrence 
of various rhyolitic lava-flows, round about an intrusive neck at Tardree 
Mountain. Some of these appear to be earlier than the basaltic flows of 
Carnearny, which are mapped as belonging to the lower series: others appear to 
be traversed by basalt dykes. But, as yet, material is wanting on which to found 
even a diagrammatic section. 
IV.—Nore on Bauxite. 
The products of decomposition of certain of the rhyolites, both of the Tardree 
and ‘Templepatrick types, suggests an affinity with the bauxitic clays and 
bauxites, which also occur in the county of Antrim. The whole question of the 
origin of the bauxites is deserving of a special investigation ; but I venture to 
append this note, as a contribution towards their fuller discussion, before leaving 
the rhyolitic area round Tardree. 
In the cutting on the west side of the road, which runs from Scolboa Upper 
down into Dunany Bog, the lithoidal lava is exposed in a soft form, pale grey, 
with brown joint-surfaces, and easily cut with a knife. It then yields the 
shining surface characteristic of a clay. The felspars are dull white and decom- 
posed, and are as sectile as the groundmass. A few grains of bipyramidal quartz 
occur, as if to prove the identity of the rock. The powder under the microscope 
shows a groundmass that has lost its structure, with a few orange granules of 
epidote, and opaque bodies which may be merely magnetite, or which may 
represent some decayed ferromagnesian constituent. The specific gravity of the 
groundmass, determined in Sonstadt’s solution, is 2°48. 
This groundmass adheres to the tongue when touched by it; and its condition, 
* Mem. to Sheets 21, 28 and 29, p. 18, footnote. 
