Geological Society of London. 381 
6. “On Perlitic Felsites, probably of Archean Age, from the Flanks 
of the Herefordshire Beacon, and on the Possible Origin of some 
Epidosites.” By Frank Rutley, Esq., F.G.S. 
The author has previously described a rock from this locality 
in which faint indications of a perlitic structure were discernible. 
In the present paper additional instances were enumerated and a 
description was given. The perlitic structure is difficult to recognize, 
owing to subsequent alteration of the rock. 
Decomposition-products, apparently chiefly epidote, with possibly 
a little kaolin, have been found in great part within the minute 
fissures and perlitic cracks. 
The author suggested, from his observations, that felsites, resulting 
from the devitrification of obsidian, quartz-felsites, aplites, etc., may, 
by the decomposition of the felspathic constituents, pass, in the first 
instance, into rocks composed essentially of quartz and kaolin; and 
that, by subsequent alteration of the kaolin by the action of water 
charged with bicarbonate of lime and more or less carbonate of iron 
in solution, these may eventually be converted into epidosites. 
He regarded it as probable that the rocks are of later Archean or 
Cambrian age. 
7. “The Ejected Blocks of Monte Somma,” Part 1, Stratified 
Limestones.” By H. J. Johnston-Lavis, M.D., F.G.S. 
Introductory.—The author referred to the Hamilton collection, now 
in the British Museum, and to the work of Prof. Scacchi, who 
enumerated 52 mineral species as having been found in the ejected 
blocks, and indicated the importance of these from a geological and 
voleanological point of view. His own collection contains over 600 
specimens, showing the graduation from unaltered limestones, through 
various stages of change into numerous varieties of ‘true meta- 
morphic rocks,” which, in their turn, shade into igneous rocks more 
and more approaching the several modifications of the normal cooled 
magma of the volcano. Moreover, such rocks come from depths 
where they have not been affected by alterations of a secondary 
nature. 
He then gave a classification of the varieties of ejected blocks. 
The Tertiary rocks are but slightly metamorphosed, whilst the lime- 
stones of Cretaceous or earlier age afford an almost unlimited series 
of mineral aggregates. Physical changes have converted them into 
carbonaceous and saccharoidal marbles; next oxides and aluminates 
have separated, and silicates have been introduced. Such rocks come 
under the definition of accidental ejectamenta. They are only ejected 
when the apex of the crater-cavity, formed by an explosive eruption, 
extends below the platform of the volcano into the underlying rocks. 
He then traced the history of the eruptions of Somma-Vesuvius 
through divers phases, showing that it was only at a comparatively 
late period that limestone-fragments were blown out, though this had 
taken place long before the Plinian eruption. The stratified lime- 
stones have been chosen for the first part of this paper, because their 
original lithological structure acts as a guide as we proceed from a 
normal limestone to its extreme modifications. 
