76 GeoJoijlcal Socleff/. 



semivitreons lavas, with their associnted agglorneratcs and ashes, 

 constituting the ridge of Ercal Hill, Lav\aence Hill, and the AVrekin, 

 and the low ridge parallel to this to the west, both of which are 

 marked as " greenstone" on the Geological-Survey Map. Their com- 

 position and structure show them to have been originall}^ identical 

 with some of the glassy volcanic rocks ejected during the most recent 

 geological periods. After noticing the geological relations of these 

 rocks, the author described the structure of modern perlitic and 

 spheiulitic rocks, and pointed out that the spheroidal balls which 

 characterize them are produced by a process of more or less con- 

 centric cracking during the contraction of the mass after it has 

 been solidified. He then indicated the characters of the ancient 

 rocks of the Lower Silurian district of Shropshire, and showed their 

 identity of structure with the modern spherulitic pitchstones and 

 perlites ; he also noticed that in some instances they had become 

 devitrified. As the result of his investigation, he says that the 

 structure of these rocks proves their original vitreous condition, for 

 the perlitic and spherulitic formations, with their associated micro- 

 litha, are only observed in connexion with the obsidian orpitchstone 

 varieties of volcanic glass — and that in the older as in the younger 

 series there is the same gradation between the vitreous and stony 

 varieties. 



June 6th, 1877.~Prof. P. Martin Duncan, M.B., P.R.S., 

 President, in the Chair. 



The following communications were read : — 



1. "On the Eank and Affinities in the Eeptilian Class of the Mo- 

 sascmridce, Gervais." By Prof. H. Owen, C.B., F.R.S., F.G.S. 



2. "Note on the Occurrence of the Remains of Hycvnarctos in the 

 Red Crag of Suffolk." By Prof. William Henry Flower, F.R.S., 

 F.G.S. 



3. " On the Remains of Hypsodon, PorilieKS^ and IcJithyodectes 

 from British Cretaceous strata, with descriptions of new species." 

 By E. Tulley Newton, Esq., F.G.S., of H.M. Geological Survey. 



4. " On the Precarboniferous Rocks of Charnwood Forest." Part I. 

 By the Rev. E. Hill, M.A., F.G.S., and the Rev. T. G. Bonney, M.A., 

 F^G.S. 



The authors described a mass of slates, grits, and volcanic brec- 

 cias, accompanied by some knolls and dykes of syenite, spread over 

 a space of about 50 square miles. They showed that the patches 

 marked on the Survey Map as Greenstone of Pardon, Birchwood, 

 and Buck Hill, except a very small portion of the latter, are really 

 altered rock, that the Syenite knoll of Bawdon Castle carries a mass 

 of breccia in its centre, aud that the area of the Syenite in Bradgate- 

 House Woods must be enlarged. 



Several writers have noticed that part of the porphyiitic region 

 of the north-west corner is altered rock. The authors showed that 

 there is in it no igneous rock at all, and that the same is the case 

 with every one of the smaller patches marked as porphyry on the 

 Survey Map. All are volcanic breccias, ashes, or agglomerates, 



