TRANSACTIONS OF SECTION C. 5 7 i 
TUESDAY, SEPTEMBER 25. 
The following Papers were read :-— 
1. Ona supposed case of Metamorphism in an Alpine Rock of Carboniferous 
Age. By Professor T. G. Bonnny, M.A., F.B.S.! 
At the base of the Carboniferous series in some parts of the Western Alps is a 
conglomerate called the poudingue de Val Orsine, the matrix of which abounds in 
mica, and is supposed by some geologists to exhibit true foliation. The author 
had examined some typical localities near Vernayaz, and stated that the fragments 
consisted of vein-quartz, gneiss, and mica schist, resembling the crystalline rocks of 
the district, with some of an unaltered purplish slate. Further, microscopic 
examination showed that the ground mass exhibited no metamorphism of 
importance, but that the mica was also of fragmental origin. He also described 
a green flinty argillite from the same district, supposed to be a member of the 
Carboniferous series, This proved to have been composed originally of fragments 
much coarser than he should have expected from the aspect of the rock. These had 
been cracked and more or less crushed in situ by the pressure to which the whole 
district has been subjected, and had then undergone certain micro-mineralogical 
changes. He concluded by stating as the result of his investigations of the Alps, 
that there is always an abrupt transition from the comparatively unmetamorphosed 
rocks of known geological age to the true schists and gneisses of unknown but 
certainly far greater antiquity, and that nothing short of the clearest proof would 
justify us in considering any of the crystalline foliated rocks of the Alps as altered 
evonian or Silurian, even if the latter term be used in its most extended sense. 
2. Note on the Nagel-flue of the Rigi and Rossberg. 
By Professor T. G. Bonney, M.A., F.R.S2 
The author called attention to the following points in regard to the conglomerate 
of these mountains:—(1) That the pebbles were not seldom indented by mutual 
pressure. This he considered, like the indentations common on the quartzite pebbles 
of the Bunter conglomerate of Central England, to be sufficient to show that such 
impressions did not indicate an early stage of metamorphism in the ordinary sense 
of that word, as argued last year by Professor James Thomson,’ but were simply 
deformations due to long-continued pressure apart from any action of heat. 
(2) That the pebbles in this district consisted mainly of grits and limestones from 
the Secondary and perhaps early Tertiary series of the Alps, with a variable 
amount of a reddish granite (of whose locality he was ignorant). Alpine schists 
and gneisses were exceedingly rare. He concluded that the nagel-flue was deposited 
by a river, whose drainage area had some correspondence with that of the present 
Reuss, and its pebbles show that this Miocene river must have flowed almost wholly 
over the more modern Alpine rocks. These have now been stripped away from 
the underlying metamorphic series over a large extent of the basin of the Reuss. 
(3) That there was a close analogy between the Bunter conglomerate and the 
nagel-fiue ; the former also resembling the British Old Red Sandstone, and a part 
of the Calciferous sandstone series in Scotland. As these three were admittedly 
fresh-water deposits, he argued that the Bunter series (parts of which had some 
resemblance to the ordinary molasse) should be reckoned among the true fluviatile 
or fluvio-lacustrine deposits. 
3. On the Pre-Cambrian Igneous Rocks of St. David's. 
By Professor J. F. Buaxe, M.A., F.G.S. 
The rocks below the Cambrian conglomerate have been described by 
Dr. Hicks as bedded rocks belonging to three distinct periods. The same rocks 
1 Published in extenso Geol. Mag. Dec. ii. vol, x. p. 507. 
2 Idem, p. 511. 
3 Report, 1882, p. 536. 
