The Rev. S. Haughton’s Notes on Mineralogy. 49 
ingly hard, striking fire freely under the hammer, but when 
subjected to long-continued action of the reducing flame of the 
blowpipe, melting slightly on the edges, particularly in_ the 
neighbourhood of the minute specks of silicate of iron which 
appear here and there through the body of the rock. 
The following analysis will serve to give an exact idea of the 
composition of this rock, which is more siliceous than the fel- 
stones of Waterford and Killarney :— 
Per cent. Atoms. 
Silicaccerr sy ye. 43.8436 aus 1:808 
Alumina... 7°86 0-151 
Peroxide of iron. 3°32 0:041 0-192 
aoe ark gece bu(OO 0:035 
agnesia. . . O45 0:022 
He a ee ee 
Seda ving! is aeeGs 0-084 
99°70 
It is evident from this analysis, that the atoms of protoxides 
and peroxides are about equal in quantity, and that the rock may 
be represented by a mixture of felspar and quartz. 
Q+F=1:808, 
From these equations, we find that its mineralogical compo- 
sition is as follows :— 
Per cent. 
GSE 6 eee ene a, Se Oe 
Orthoclase felspar. . . 5416 
99°70 
2. Siliceo-felspathic Rocks of Knockmahon, Co. We ater ford. 
The felspathic rocks of Knockmahon are intimately associated 
with the copper lodes which have rendered that locality famous, 
and occur abundantly on the shore below the village of Bon- 
mahon in prismatic masses of a columnar structure, which have 
received the name of the Bishop’s Library. These rocks occur 
also, and are well shown, in a cutting for a tramroad connecting 
Tankardstown with Knockmahon Mine. In this latter locality 
they occur stratified conformably with the brown fossiliferous 
Silurian slates which are found at the Tankardstown Mine. The 
following analysis is of a specimen taken from the stratified 
siliceo-felspathic rocks of the cutting of the tramroad :— 
Phil. Mag. S. 4. Vol. 14, No. 90, July 1857. 19 
