94 Cote— The Rhyolites of the County of Antrim ; with a Note on Bauxite. 
I have no doubt that this glassy rhyolite forms part of a lava-flow, comparable 
to those in the Tepla valley, between Skleno and Hlinik, where perlites* and 
pitchstones are exposed in cliffs more than a hundred feet in height. 
Since the plane of junction between the pitchstone and the overlying lithoidal 
rhyolite is parallel to the planes of fissility in the latter, it is highly probable that 
the fissile structure is here an indication of flow. Unlike the rock of Temple- 
patrick, however, there is no delicate banding present to emphasise and confirm 
this observation. 
If, however, we stand at the Tardree Inn, and look up, somewhat towards the 
right, at the steep brae on the north, a pale quarry is seen on the road rising to 
Sandy Braes. We have here a crumbling and altered rhyolite, with the most 
beautiful banded structure; its general colour is pink, with yellower layers, and 
the flow-planes, as seen in this east-and-west section, are horizontal or gently 
undulating. The rock goes to pieces under the hammer, and reminds one, in 
some ways, of the altered rhyolitic andesite of Tay Bridge End, to which 
reference has already been made. (PI. IIL., fig. 2.) 
We are now in the townland of Barnish, which includes the plateau of Sandy 
Braes, certainly one of the most interesting spots for the geologist in the whole of 
Ireland. Bergert long ago examined on this spot ‘‘ pitchstone porphyry” and 
‘‘pearlstone porphyry,” and Portlock { referred to the “mineral” pitchstone as 
‘‘abundant in the porphyry of Sandy Braes, accompanied by Pearlstone.” Von 
Lasaulx § knew these glassy rocks only in collections, styling them Obstdianporphyr ; 
and Mr. W. W. Watts|| has made a very careful microscopic study of certain 
specimens from ‘‘ Connor, Sandy Braes.” Probably, by-the-by, the order of these 
two names should be reversed. ‘The general aspect of the rocks of Sandy Braes 
has been touched on recently by Messrs. M‘Henry and Watts 4] and by myself.** 
The plateau derives its name from the sand produced by the decomposition of 
the rhyolites, sand of any kind being scarce in this region. The rubbly products 
*Tt would be unnecessary to point out the origin of this term, had not both Mr. Watts and Mr. 
Smeeth recently applied it to the minute globules into which the glass becomes divided upon contraction. 
This is only adding a new element to the confusion which has been imported into petrographical nomen- 
clature. Perlite was invented by Beudant—‘‘ Voyage en Hongrie” (1822), tome i., p. 829—as a French 
translation of perlstein, and to take the place of Haiiy’s less obvious word perlaire. It is the name of a 
rock having a particular structure ; the globules in that rock might be called ‘ pearls,” but certainly not 
“ perlites.”’ 
+ Op. cit., Trans. Geol. Soc. London, ser. i., vol. iii. (1816), p. 190. 
+ “Report on the Geology of the County of Londonderry, &c.” (18438), p. 212. 
§ Op. cit., Tscherm. Mitth., Bd. i., p. 418. 
|| “Note on the Occurrence of Perlitic Cracks in Quartz,” Quart. Journ. Geol. Soc. London, vol. 1. 
(1894), p. 367. 
q ‘« Guide to the Coll. of Rocks, &c., Geol. Survey of Ireland” (1895), p. 80. 
** «The Volcano of Tardree, County Antrim,” Geol. Mag., 1895, p. 305. 
