Royal Geological Socicty of Ireland. 187 
The rocks exhibit evidence of alteration and of silicification, 
suggesting that the district may have passed through a Solfatara 
stage, and that its condition may have been not far removed from 
that of a geyser region. Perlitic structure is common, and is often 
found in connection with spherulitic growth, of which there are 
many gradations, and specially marked and large examples are 
presented in the agate nodules. 
Some nodules seem to result from spheroidal fracture, others to 
be masses of flow-brecciation; but the majority have a spherulitic 
crust, often surrounding an interior occupied by secondary quartz 
or chalcedony. Similar specimens were described and compared, 
which had been received from Boulay Bay, through the kinduess of 
Professor Bonney. The evidence of these and of the Lleyn ex- 
amples appears to be strongly in favour of the view that the 
spherulite is the least altered and most durable part of the mass. 
Other considerations were brought forward by the author, which 
would offer some further difficulties in accepting the decomposition- 
theory to account for the origin of the interior of the nodules. 
Some of the specimens described present certain special character- 
istics, and, at one locality in the Lleyn, what seem to be quartzose 
amyegdaloids occur, in close relation to agate nodules. On the whole, 
although the mode of origin is difficult or impossible definitely to 
prove, the evidence appears to suggest that in these nodules a 
spherulitic crust has formed around an originally vesicular nucleus. 
3. “On the Action of Pure Water, and of Water saturated with 
Carbonic-acid Gas, on the Minerals of the Mica Family.” By 
Alexander Johnstone, Esq., F'.G.S. 
Two muscovite fragments were suspended for a year, one in dis- 
tilled water, the other in water saturated with carbonic anhydride. 
A good deal of mica-dust was detached from each, but no material 
had been dissolved, the only chemical change being hydration, 
accompanied by physical alteration, producing a mineral chemically 
and physically similar to a natural hydromuscovite. 
When biotite was similarly treated, the mineral suspended in 
the distilled water became a hydrobiotite, whilst that in the water 
saturated with carbonic anhydride underwent chemical change, and 
was converted into hydromuscovite by loss of magnesia and iron, 
which were dissolved in the water. 
Lepidomelane in pure water became hydrated, but in carbonated 
water also sustained a loss of iron. 
The author has ascertained that when anhydrous micas become 
hydrated, or lower hydrated ones more highly hydrated, they increase 
in bulk. 
Royat GeonocicaL Soctrty oF [RELAND. 
HE Annual General Meeting for the election of officers took 
place at the rooms of the Royal Dublin Society on the 20th of 
February. Mr. A. B. Wynne, F.G.S., was elected President and 
addressed the meeting, taking two of the most important questions 
recently brought under the notice of geologists, as his subject, 
