740 Scientific Proceedings, Royal Dublin Society. 
rather to raise the value of the density than to reduce it. The 
analysis is as follows :— 
Percentage. 
Si02, . ‘ : : , 5 - $ 90-63 
Al20s, : : i 5 ; ‘ 3 1-79 
Fe203, : 4 6 5 ° - : 0°34 
CaO, . 5 , 4 : 4 ; F 4°45 
MgO, . : ‘ : : ‘: = i 0:14 
LiOz, NazO and K,0 \ 9-51 
calculated as Na,2O, cease’ 
99°86 
This caleedony character of the quartz may reasonably be 
taken as pointing to extensive thermal action along the main lines 
of fracture, and would receive a certain amount of illustration 
from the similar phenomena presented by certain quartzite beds 
which occur in the Carboniferous formation of St. Etienne (Loire), 
and which I was enabled to examine and have explained to me 
by Monsieur de Grand d’Eury during an excursion to that mining 
district with the French Association for the advancement of 
science, which took place last August. In this case the alteration 
of the rock into calcedony is manifest and clear in all its stages, 
and as I was informed by M. de Grand d’Hury, accompanied by 
the concentration of titanic acid in certain zones and the consequent 
presence of the minerals therein usually representing that acid. 
It is worthy of note that the district of St. Etienne possesses 
several gaseous mineral springs of noted quality in the country, 
which may be taken as the residual efforts of the forces which have 
left such marked results in the alterations and derangements of the 
strata so well studied by the eminent geologist already mentioned. 
It would be desirable that the whole of the quartzites of the 
Co. Wicklow and of the neighbourhood of Dublin be examined 
carefully and comparatively from the point of view of constitution 
and the alterations which they have undergone at their contacts 
with other rocks in different localities of the districts mentioned. 
EXPLANATION OF PLATE XXyYV. 
Figs. 
1. Brookite, from Quartzites, Shankill, Co. Dublin; forms pre- 
sented: ¢=2P 0; y=1 Pm; e=P2; I= Po. 
2. Anatase, from Quartzites, Shankill, Co. Dublin. 
