ON THE MINERALOGY OF THE COUNTIES OF DUBLIN 
AND WICKLOW. 
BY 
The Rey. SAMUEL HAUGHTON, ».v., Dublin; p.c.u., Oxon.; 
Professor of Geology in the University of Dublin, 
[Read March 18, 1878.] 
The most convenient method of describing the minerals that 
occur in these counties, is to state in succession the minerals 
that are found in each of the several rock formations, referred to 
by the Rev. Maxwell Close, in his sketch of the Geology of the 
neighbourhood of Dublin. 
1. THE MINERALS OF THE DUBLIN AND WICKLOW GRANITES. 
These minerals are twofold. 
(A) The Constituent Minerals, 
(B) The Accidental Minerals, 
(A) The Constituent Minerals, The granites of Dublin and 
Wicklow are quinary, consisting of the following minerals :— 
1. Quartz. 
2. Orthoclase Feldspar. 
3. Albite Feldspar. 
4, Margarodite Mica. 
5. Lepidomelane Mica. 
1, The Constituent Quartz is grey, watery, transparent, and 
has a mean specific gravity = 2°645. 
2. The Constituent Orthoclase Feldspar is milk white, opaque ; 
and has a mean specific gravity = 2°540, 
Its mean chemical composition, taken from seven specimens, 
of which three were from Dublin localities, and four from Wick- 
low localities, is as follows :— 
Orthoclase (mean of seven Specimens.) 

Silica, ° . ° 64:59 per cent. 
Alumina, . ° ° 18°31 ms 
Lime, : . : 0:25 + 
Magnesia, ‘ 2 - 0:58 " 
Potash, a 2 e 12-23 ” 
Soda, ‘ ‘ ‘ 2°75 4 
Loss by ignition, . ; 0:58 3 
99.29 
