362 Geological Society. 



2. " On some Nodular Felstones of the Lleyn Peninsula." By 

 Miss Catherine A. Eaisin, B.Sc. 



This paper dealt with two small masses of rock forming the head- 

 lands of Pen-y-chain and Careg-y-defaid, a few miles from PwUheli. 

 They consist of old lava-flows, once glassy, now devitrified and, at 

 the former place, associated with iuterbedded agglomeratic and ashy 

 strata. The lithological characters, as well as other slight evidence 

 obtained, would fully support the identification by the Survey of 

 the surrounding beds as of Bala age. 



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 connexion 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 kindness 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 ofl'er 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 

 amygdaloids occur, in close relation to agate nodules. On the 

 whole, although the mode of origin is difficult or impossible defi- 

 nitely 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 hydromusoovite. 



When biotite was similarly treated, the mineral suspended in 

 the distilled water became a hydrobiotite, whilst that in the water 



