114 Cotr——The Rhyolites of the County of Antrim; with a Note on Bauxite. 
have proved of constant service ; and the diffusion-column, devised by Prof. Sollas, 
has often reduced a task of considerable labour to one both of delicacy and pleasure. 
It will have been seen that the rhyolites of the county of Antrim are as a rule 
poor in ferromagnesian constituents, but that the occurrence of these minerals 
divides the rocks into two groups, the biotite-rhyolites, such as those of Temple- 
patrick, Kirkinriola, and Ballycloughan, and the augite-rhyolites, represented on 
Carnearny and Sandy Braes. All the types, whatever their structure, are fairly rich 
in porphyritic constituents, with the exception of the fluidal rhyolite of Cloughwater. 
The banded, fluidal, and perlitic structures in these rhyolites are probably 
unsurpassed by those of any other lavas in the British Isles; but spherulitic 
structure is certainly uncommon. 
The various glassy and fluidal lavas round about the dome of Tardree Moun- 
tain probably flowed from that centre, and at one time built up a true volcanic 
cone around it. 
This view is strengthened by the occurrence of a volcanic agglomerate on 
Sandy Braes. 
The only section in which evidence as to the sequence in time and actual 
relations of the rhyolites and the plateau-basalts can be obtained is the western 
part of the quarry at T’emplepatrick. Here the rhyolite is intrusive between a 
mass of basalt and the chalk, along the line of the flint-gravels, and it includes, 
somewhat obscurely, a lump of basalt near its upper margin. ‘The conglomerates 
of Glenarm and Ballypalady, with pebbles of rhyolite, occurring between the 
Lower and the Upper Basalts, merely prove that the rhyolites were intruded or 
extruded prior to the formation of the Upper Basalts ; they prove nothing regarding 
the relations of the rhyolites and the Lower Basalts, unless it can be shown that 
they are tuffs and not ordinary conglomerates. 
From the relations of the bauxite of Glenarm to the underlying rhyolitic 
conglomerate, and from the general type of decomposition of the lithoidal rhyolites, 
it is suggested that the pale bauxites may have originated in the alteration of 
rhyolites or rhyolitic ashes. 
Finally, I must express my thanks to those active members of the Belfast 
Naturalists’ Field Club who have so generously helped me in the field or with 
photographs of the sections visited:—Miss M. K. Andrews, Mr. W. J. Fennell, 
Mr. Wm. Gray, m.x.1.4., Miss 8. M. Thompson, and Mr. R. Welch. I am specially 
indebted to Mr. A. M‘Henry, m.R.1.4., of the Geological Survey of Ireland; to 
Mr. J. St. J. Phillips, a.n.1B.4., of Belfast, for permission to reproduce two of 
his admirable photographs; to Mr. A. P. Hoskins, F.1.c., for his quantitative 
chemical work; to Mr. T. D. La Touche, of the Geological Survey of India, who 
helped me, during his stay in Dublin, in the delicate observations with the diffusion- 
column; and to my Wife, for determining the specific gravity of the typical 
specimens, and for the microscopic drawings which accompany the present paper. 
