

[ 141 ] 

 XYIL Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 74.] 



May 10, 1832.— J. Y\ Hulke, Esq., F.E.S., President, 

 in the Chair. 



T^HE following communications were read : — 



-*- 1. " On the Belations of Hybocrinus, Baerocrinus, and Hybo- 



cystites." By P. Herbert Carpenter, Esq., M.A. 



2. " On the Madreporaria of the Inferior Oolite of the neigh- 

 bourhood of Cheltenham and Gloucester." By B. E. Tomes, Esq., 

 E.Ct.S. 



8. " On the Exploration of two Caves in the neighbourhood of 

 Tenby." By Ernest L. Jones, Esq. 



4. " Note on the Comparative Specific Gravities of Molten and 

 Solidified Yesuvian Lavas." By H. J. Johnston-Lavis, Esq., E.G.S. 



Erom some experiments made on Yesuvian lava, Prof. Palmieri 

 in 1875 expressed the opinion that its specific gravity, when molten, 

 might be as high as 5-0, though when cooled it is only 2-7. The 

 author described the results of experiments made in December 188 L 

 on some lava flowing across the Atrio del Cavailo. Favourable cir- 

 cumstances enabled him to gain a position above a perfectly molten 

 stream, the surface of which was protected from radiation by the 

 heated walls of a tunnel which the lava had already formed by 

 cooling of the crust. Onto this were dropped, from a heigbt of 

 \\ yard : — (a) light scoria : this floated on the surface until lost to 

 view (the stream could be watched for 150 yards or so) ; (6) fairly 

 solid lava, with some vesicular cavities ; this slowly sank, until 

 after some distance it disappeared ; (c) the most compact lava that 

 could be found, in which, however, were a few small cavities ; this 

 sank rapidly, the molten rock welling up round it. The author 

 considered that these experiments demonstrate that the cooled lava 

 is more dense than the molten, and that the apparently contra- 

 dictory results obtained by Prof. Palmieri were due to the fact that 

 the surface of the stream, by loss of heat, had become viscid, so 

 that the solid material floated, though of greater density. The 

 author concluded by citing other confirmatory evidence of his view. 



May 24.— J. W. Hulke, Esq., E.E.S., President, 

 in the Chair. 



The following communications were read : — 

 1. "On the Geology of Costa Pica." By George Attwood, Esq., 

 E.G.S., E.C.S., Assoc. Memb. Inst.C.E. ; with an Appendix by W. 

 H. Hudleston, Esq., M.A., E.G.S., E.C.S. 



The author commenced his journey at the town of Punta Arenas, 



