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of being converted into serpentine, aids in forming the hornblende. 

 Further, there are dykes and veins over the same area of a dark 

 trap. Some of these are augitic, others hornblendic. The author 

 believes that at any rate in certain of these the hornblende is of 

 secondary formation. On the west coast are veins of granite ; those 

 on the east coast, said to be granite, prove, on careful examination, 

 to be altered rock, remarkably like granite veins, but not really such. 



In discussing the origin of the sei-pentine, the- author called atten- 

 tion to a structure commonly seen, which appeared to be a true 

 "fluidal structure." He then described the result of microscopic 

 examination of many specimens of the Lizard and some other ser- 

 pentines. Commencing with slightly altered Lherzolite (from the 

 Ariege), he traced the change through the older gabbro of Coverack 

 to the serpentine rock of that place, which contains a large quantity 

 of unaltered olivine ; and so to other serpentines in which the 

 olivine is quite replaced by the mineral serpentine. He described 

 also the mode of the change. The other minerals found in the 

 serpentine rock are enstatite, varieties of augite, and occasionally a 

 fair quantity of picotite, with, of course, oxides of iron. Hence he 

 concluded that, as had been already shown as regards some other 

 serpentines, that of the Lizard was the result of the hydrous altera- 

 tion of an olivine rock, such as Lherzolite. 



4. " On certain ancient Oevitrified Pitchstones and Perlites from 

 the Lower Silurian District of Shropshire." By S. Allport, Esq., 

 F.G.S. 



In this paper the author described a series of ancient vitreous and 

 semivitreous lavas, with their associated agglomerates and ashes, 

 constituting the ridge of Ercal Hill, Lawrence Hill, and the Wrekin, 

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

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

 composition and structure show them to have been originally 

 identical with some of the glassy volcanic rocks ejected during the 

 most recent geological peiiods. After noticing the geological rela- 

 tions of these rocks, the author described the structure of modern 

 perlitic and spherulitic rocks, and pointed out that the spheroidal 

 balls which characterize them are produced by a process of more or 

 less concentric 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 pei'lites ; 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 microliths, are only observed in connexion with the 

 obsidian or pitchstone varieties of volcanic glass ; and that in the 

 older as in the younger series there is the same gradation between 

 the vitreous and stony A'arieties. 



IL— June 6th, 1877.— Prof. P. Martin Duncan, M.B.,. F.RS., 

 President, in the Chair. — The following communications were read : — 



