Bean) 
III. 
THE RHYOLITES OF THE COUNTY OF ANTRIM; WITH A NOTE ON 
BAUXITE. By GRENVILLE A. J. COLE, M.R.LA., F.G.8., Professor of 
Geology in the Royal College of Science for Ireland. (Plates III. and IV.) 
{ Read Drcemprr 18, 1895. | 
I.—IntTRopDUCTION. 
Tue occurrence of small exposures of igneous rock in the county of Antrim, entirely 
differing in character from the normal basalts of the district, has long been known 
to field-observers. Dr. Jean Francois Berger,* of Geneva, author of so many 
contributions to the geology of the British Isles, paid particular attention to the 
“‘Clay-porphyry” of Tardree Mountain and of Ballycloughan, and to the glassy 
rocks of Sandy Braes; while Captain J. KE. Portlock,t in his early surveys, came 
across ‘‘trachytic porphyry” in both the counties of Antrim and of Down. 
J. Brycet{ was probably acquainted with this rock under the name of “ grey- 
stone,” a term commonly used for trachytes ; but more than fifty years had elapsed 
since the publication of Berger’s paper before any additional information was 
obtainable as to its true character. KE. T. Hardman,§ on the basis of his own 
elaborate analysis, then placed the rock of Tardree with the rhyolites of von 
Richthofen ; Professor Hull,|| at a time when there were few students of thin 
sections, described its microscopic characters; and Mr. G. H. Kinahan {| subse- 
quently referred it to the ‘‘ Nevadites.” 
It was still reserved for a German visitor, Professor A. von Lasaulx,** to make 
a careful mineralogical investigation of the rock; and, even then, the remarkable 
* «On the Geological Features of the North-Eastern Counties of Ireland’”’; with an introduction and 
remarks by the Rev. W. Conybeare. Trans. Geol. Soc. London, ser. i., vol. 11. (1816), pp. 186, 189, &e. 
t ‘(On the Study of Geological Phenomena in Ireland,” Journ. Geol. Soc. Dublin, vol. i. (1834), p. 9. 
t ‘Geological Structure of the Counties of Down and Antrim,” Report British Association, 1852, 
Notices and Abstracts, p. 42. 
§ ‘On the Analysis of Trachyte Porphyry from Tardree Quarry, near Antrim,” Journ. Royal Geol. 
. Soe. Ireland, vol. iii. (1870-3), p. 82. The paper was read in 1871. 
|| Memoir to sheets 21, 28 and 29, Geol. Survey of Ireland (1876), pp. 18 and 44. 
4 ‘‘ Manual of the Geology of Ireland” (1878), p. 208. 
** « Petrographische Skizzen aus Irland,” Tschermak’s Min. u. Petr. Mittheilungen, Bd. i. (1878), 
p. 410. 
TRANS. ROY. DUB. SOC., N.S. VOL. VI., PART III. N 
