30 Scientific Proceedings, Royal Dublin Society, — 
Chemical Analysis.—Mr. E. T. Hardman has already made an 
analysis of the rock, which has also been printed by Professor E. 
Hull in the Explanation to sheets 21, 28, 29, page 18 of the Irish 
Geological Survey. J. Roth in his excellent collection of analysis of 
rocks also cites* the analysis of Mr. Hardman, and places the rock 
of Tardree among the liparites. He remarks on the small amount 
of alumina in the analysis, the proportion of which is shown in 
the table. It seemed to me useful (principally with regard to 
Mr. Hardman’s opinion, that the felspar—originally a normal 
orthoclase—was being gradually transformed into a lime felspar) 
to conduct an analysis of the sanidine, of which it is very easy 
to obtain sufficient fresh and unaltered material out of the rock. 
Tue analysis gave the following results :— 
i II. 
si0,, 76-961 64:66 
JNO) 3 : : 5 101 sigh 
OE ee ie oak \ 20:03 Very little iron. 
CaO, é é : 7-064 1-21 
MgO, . : 0-295 — 
K,0, : : : 4-262 8-61 
NasO} | : c 1-818 5-44 
Loss by ignition, . 2:102 —_ 
Phosphoric acid, < Trace. — 
99-943 99-95 
When we consider the mineral constitution of the rock as ob- 
tained by the microscopical analysis, we may admit that only 38 
per-cent. of free silica (quartz and tridymite) and 62 per-cent. of 
sanidine were the proportion of the mixture of those constituents. 
We find in the rock 76-052 of silica, agreeing with Mr. Hardman’s 
analysis. But the same proportion of mixture requires 12-4 per- 
cent. alumina, 5°34 per-cent. potash, and 3°57 scda, all numbers 
much higher than those obtained by Mr. Hardman. The pre- 
sence of epidote makes the presence of a greater amount of lime 
intelligible, but requires an equally higher per centage of alumina. 
The great loss by ignition supports the supposition, that the rock 
analyzed by Mr. Hardman, was not fresh and unaltered. The 
increase of lime, and the decrease in alumina, potash, and soda must 
be put to the account of the decomposition. 
The high per-centage of silica in Mr. Hardman’s analysis is 
only explicable by the presence of tridymite in the paste; the 
quartz enclosed in the rock alone is not sufiicient to yield it. 
» J. Roth—Beitriige zur Petrographie der plutonischen Gesteine. Lerlin, 1873; p, 
XxXxiil. 
