124 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 1 894, 



The first of Miss Raisin's papers relates to the Nodular Felstones 

 of the Lleyn. Not far from Afonwen Junction, on the south coast 

 of this extreme promontory of Caernarvonshire, is a mass of igneous 

 rock marked on the Geological Survey map ' Felspar-porphyry 

 (intrusive) with agate-nodules.' The Author considers that the 

 character of the rocks clearly negatives the theory of intrusion ; 

 they are old lava-flows, once glassy, now devitrified, and at Pen-y- 

 chain are associated with interbedded agglomeratic and ashy strata. 

 The mass of felstone near Pwllheli also contains similar nodular 

 inclusions. These rocks must be classed as petrosiliceous, many 

 structures being probably due to secondary devitrification. Every- 

 thing, says Miss Raisin, points to subsequent silicification with 

 attendant radialization in some cases. She suggests the percolation 

 of heated waters carrying silica in connexion with the declining 

 vulcanicity or solfatara-stage of the district. 



These so-called ' agate-nodules ' have long ago attracted attention. 

 The large spherulites seem to have been developed either along 

 certain strata or within masses of flow-brecciation, those near to- 

 gether being fairly equal in size. The spherulite seems to be the 

 most durable part of the rock, which usually exhibits an originally 

 vesicular character. The matrix surrounding the nodular spheru- 

 lites consists for the most part of what must have been a compact, 

 laminated, glassy lava, now devitrified, generally perlitic, and often 

 spherulitic. The interior of the nodule is in many cases filled with 

 chalcedony, and is not distinguishable in form from an original 

 vesicle of the lava. These nodular structures are classed under the 

 following groups: — contraction-spheroids, or magnified perlitic 

 structure ; masses resulting from flow-brecciation ; solid spherulites 

 or pyromerides ; agate-nodules with an outer spherulitic crust : 

 quartzose amygdaloids ; and lastly spheroidal formations developed 

 round a nucleus, such as an agate-nodule, a group of crystals, or an 

 original vesicle of the lava. 



With regard to the second of Miss Raisin's papers, I would 

 remark that the subject of Variolite has latterly assumed consider- 

 able interest and importance amongst British geologists, both from 

 the fact that this remarkable rock has been discovered at more than 

 one point in the United Kingdom, and also because it has formed 

 the basis of some important communications to the Society. A very 

 brief allusion to two papers relating to foreign localities may not be 

 altogether out of place in this connexion. 



Thus, in their paper on the Variolitic Rocks of Mont Genevre, 



