332 
Reports and Rroceedinrjs- 
of being converted into Serpentine, aids in forming tlie bornblende. 
Furtker, there are dykes and veins over tbe same area of a dark 
trap. Some of these are augitic, others bornblendic. The autkor 
believes that at any rate in eertain 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 Serpentine, 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 Lkerzolite (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 desci'ibed 
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 sliown as regards some other 
serpentines, that of the Lizard was the result of the hydrous altera- 
tion of an olivine rock, such as Lkerzolite. 
4. “ On eertain ancient Devitrified 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 
eomposition and structure sliow them to have been originally 
identical with some of the glassy volcanic rocks ejeeted during the 
most recent geological periods. 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 ckaracterize them are produced by a process of more or 
less concentric Cracking during the contraction of the mass after 
it bas been solidified. He then indicated the charaeters of the 
ancient rocks of the Lower Silurian district of Shropshire, and 
sliowed their identity of structure with the modern spherulitic 
pitclistones 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 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 varieties. 
II. — June 6th, 1877. — Prof. P. Martin Duncan, M.B., F.R.S., 
President, in the Okair. —The following Communications were read : — 
