Cote—The Rhyolites of the County of Antrim ; with a Note on Bauxite. 87 
character. In a later passage he even styles the structure microgranitic. Mr. J. 
J. H. Teall* again reversed von Lasaulx’s decision, pointing out that the matrix 
could not be resolved, and could only be described as eryptocrystalline. 
Von Lasaulx described the rock as a quarzsanidintrachyt} or quarzsanidinrhyolit,t 
and enumerated, as the crystalline constituents, grey and black quartz, sanidine, 
small laths of plagioclase (determined as andesine by their extinction-angles), 
dark mica, tridymite, magnetite, epidote, and apatite. Dr. Bettendorf§ supplied 
an analysis of the sanidine, showing it to be distinctly a soda-orthoclase, such as 
commonly occurs in rhyolites. The soda, indeed, constitutes 5-44 per cent. of the 
sanidine, and the potash 8°61 per cent. Prof. Hull|| had previously shown the 
presence of dark mica, and hornblende is recorded both by Mr. Hardman and 
Mr. Watts. The latter writer regards the plagioclase that is present as albite, 
and adds zircon, rutile, and sphene as constituents of the rhyolites of this 
area, 
The typical rock was analysed in 1871 by Hardman,** who reported an 
unusually high proportion of lime, and a correspondingly low amount of alumina. 
He believed that lime had been imported into the mass during its alteration. Dr. 
Bettendorf found 1°21 per cent. of lime in the porphyritic orthoclase; and von 
Lasaulx pointed to this mineral, and to the epidote formed at its expense, as the 
source of Hardman’s 7 per cent. of lime in the rock as a whole. Prof. J. Roth, tt 
while commenting on the low amount of alumina, placed the rock, with Hardman, 
among the liparites or rhyolites. Mr. Player,f{ however, subsequently obtained 
results differing markedly from those recorded for the alumina and lime, but 
agreeing closely as regards the other constituents. We may take his analysis, 
then, as that of the normal rock, which thus becomes a representative rhyolite. 
It is well to again emphasise this fact, since the rock of Tardree has been so 
freely called a trachyte, a’ trachyte-porphyry, and even a trachyte-porphyrite. 
The fragments of highly silicated lavas, on the other hand, found in Mull,§§ with 
specific gravities of 2°45 to 2°50, and of similar age to the rhyolites of the 
county of Antrim, remain among the very few representatives of true trachyte 
in our islands. 
* « British Petrography”’ (1888), p. 348. } Tsch. Mitth., 1878, p. 418. 
{ ‘Aus Irland,” p. 167. § Tsch. Mitth., 1878, p. 417. 
|| ‘‘ Mem. Geol. Survey,” Sheets 21, 28 and 29, p. 18. 
{ Watts, ‘‘ Note on the Occurrence of Perlitic Cracks in Quartz,” Quart. Journ. Geol. Soc. London, 
vol. l., p. 868 ; and M‘Henry and Watts, ‘‘ Guide to the Collections of Rocks and Fossils, Geol. Survey 
of Ireland” (1895), p. 80. ** Op. cit., p. 29. 
tt ‘ Beitrige zur Petrographie der plutonischen Gesteine” (1873), pp. 111 and xxxii. 
tt See Teall, “ British Petrography” (1888), p. 348. 
§§ G. Cole, “‘Note on the Gravel of Ardtun,” Quart. Journ. Geol. Soc. London, vol. xliii. (1887), 
p. 277 Q 2 
