92 Cote—The Rhyolites of the County of Antrim ; with a Note on Bauvite. 
the rubbly exposures in the road upon the south. A small plantation now runs 
along the east side of the little valley which divides this crest from Carnearny. 
On the west side, however, the same fissile rhyolite is clearly marked along a line 
of miniature cliffs. Possibly this is the spot represented in fig. 4 of the Survey 
Memoir, which is not localised, and which is described as ‘‘ Quarry of 'Trachyte 
porphyry and Rhyolite.” As the word “rhyolite” is not used elsewhere in the 
memoir, it is impossible to know the type of rock to which, in this instance, it was 
intended to refer. ; 
However, two types are shown in juxtaposition in this interesting valley-side. 
The planes of division here dip about 10° westward, the Tardree massif lying to 
the north-east. ‘The upper part of the section is composed of lithoidal rhyolite, 
like that of the opposing brae, weathering in a platy fashion, and with the usual 
porphyritic crystals; the lower part is dark, and at first sight resembles the 
basaltic boulders of the slopes of Carnearny. Outwardly, however, it reveals 
spherulitie and perlitic structures, and, when chipped, at once proves to be a 
deep grey pitchstone, containing handsome brown spherulites, which are from 
4mm. to 20 mm. in diameter. On fracture, they appear somewhat dull and 
earthy. 
In microscopic section, these spherulites are only slightly differentiated from 
the glass, like those in some Icelandic rhyolites, or m the fluidal pitchstones of 
Zwickau, or—a still more striking instance—in the well-known lithoidal andesite 
of the Stefanschacht near Selmeczbinya. ‘They are darker in colour than the 
ground, from which they may be divided by a shrinkage-crack. They have no 
radial structure, and are simply more crystalline knots in the matrix, which have 
already begun to undergo some oxidation and decomposition.* (Pl. IV., fig. 2). 
The matrix is perlitic, the main cracks being iron-stained ; but the spiral 
cracks are waved and irregular, not clean and sharp as usual. It is impossible to 
ascertain that they actually traverse any of the microlites of the groundmass, and 
I believe that their irregularity is due to their being interfered with by the larger 
of these tiny prisms, and by groups of them. The microlites consist, firstly, of 
rods of felspar, in many cases bifurcated at their growing ends and square in 
cross section ; secondly, of far smaller prisms of pale green pyroxene, some of them 
showing the re-entrant angle at one end, due to twinning on the orthopinacoid. 
These pyroxenes alter to a yellow colour before the felspars exhibit any change. 
Thirdly, magnetite is fairly abundant. The glass in which the microlites le is 
pale brown and singularly pure ; a few globulites alone appear in it, often 
arranged in lines. ‘The microlites, however, form a far larger part of the ground- 
mass than does the glass. 
* Compare G. Cole, ‘On Hollow Spherulites,’’ Quart. Journ. Geol. Soc. London, vol. xli. (1885), 
pp- 165 and 166. 
