80 Cotp—The Rhyolites of the County of Antrim; with a Note on Bauxite. 
removed from a true glass. The ferromagnesian constituent, as at the chalk- 
quarry, is biotite, occurring in dark little flakes, only in part identifiable. A 
colourless mineral, characterised by minute rectangular and, more rarely, 
hexagonal sections, and by low polarisation-colours, is equally abundant. A 
few of these crystals are simply twinned; but their small size renders the deter- 
mination of their uniaxial or biaxial nature impossible. They mostly show a 
zonal structure, and many of their characters thus suggest nepheline. A sample 
of the rock was consequently roughly powdered, was boiled in concentrated 
hydrochloric acid, and was allowed to stand for twenty-four hours. It became 
thoroughly bleached ; but no gelatinisation occurred on evaporation, and the same 
small crystals, with low polarisation-colours, remained unaltered in the residue. 
Hence I conclude that they are merely a form of the sanidine which prevails in 
the coarser varieties of the Antrim rhyolites, and their occasional twinning also 
supports this view. In the residue from the digestion in acid, a few grains of 
quartz and epidote appeared, after the finest material had been washed away. 
From the variation in character of the specimens obtainable at Templepatrick, 
I suspect that we have to deal, as at Tardree, with a complex group of rhyolites, 
part only of which forms the central intrusive core. The wavy flow-structure 
and brecciation at the churchyard certainly suggest a lava erupted at the surface. 
But any pitchstones or obsidians that may exist in this area still lie hid. I do 
not understand the description* of the “‘ pearlstone” found ‘‘on the upper side 
of the railway,” which was said by Mr. Duffin to be “almost all felspar of a 
compact texture, and of a pearl-grey colour”; possibly the name “‘ pearlstone ” 
is here misapplied. Professor Hull goes on to speak of ‘the pitchstone of 
Templepatrick,” possibly on the basis of Mr. Duffin’s notes. For my own part, 
I have failed to find exposures south of the railway, and know of no glassy rock 
in this locality. 
The mode of occurrence of the compact rhyolites of emplepatrick has given 
rise to some difference of opinion. In the Memoir to Sheets 21, 28, and 29 of 
the Geological Survey of Ireland, published in 1876, no reference is made to the 
remarkable sections in the chalk-quarry. The wells referred to on p. 21 of the 
memoir are now both closed; but the existence of the rhyolite beneath the 
churchyard is still proved, as we have seen, whenever graves are dug. The 
critica] sections are certainly at the present time in the large quarry; but the 
representation of these in the longitudinal section,+ published in 1891, is hardly 
satisfactory. A large dome of rhyolite (‘‘ Trachyte porphyry ”)is shown south of 
the railway, while the mass exposed in the quarry is represented as an isolated 
fragment. It may be observed that the earlier sections of the Irish Survey were 
* Memoir to sheets 21, 28 and 29, Geol. Survey of Ireland, p. 21. 
} Geol. Survey of Ireland, Long. Sections, Sheet 31. 
