TRANSACTIONS OF SECTION C. 1029 
10, Although the crushing of a crystalline rock in situ, or the squeezing and 
shearing of a breccia or conglomerate of crystalline fragments, occasionally gives 
rise to local difficulties, these are on a small scale, and sedimentary beds belonging 
to the Paleeozoic or later periods of deposition are generally readily distinguishable 
from the whole of the crystalline series. Though folded and faulted in the most 
extraordinary manner, the members of the two series can generally be separated, 
and in the Alps there is no evidence of a mingling of the one with the other in the 
process of rolling out or squeezing together ; so that after patient study and micro- 
scopic examination we can generally decide without hesitation whether a particular 
set of rocks has originated from the crystalline or the sedimentary series. I do not 
say that we can always decide whether a schist or a gneiss has originated from an 
igneous rock or from an older schist or gneiss, but I think that in the Alps we can 
say that it has originated from one of these. Fortunately, intrusive rocks are very 
rare in the Paleeozoic and later deposits in this part of the Alps. 
11. Thus, although the Tertiary metamorphism of the Alpine rocks is very 
important, it is more pretentious than real, and its effects seem to have been the 
greatest where it has found a rock already crystalline to act upon. Hence I believe 
that every true gneiss and schist in the Alps is much older than the Carboniferous, 
and is probably older than any member of the Paleozoic period. 
4, Some Examples of Presswre-Fluxion in Pennsylvania, 
By Professor H. Carvin Lewis. 
The three localities in Pennsylvania described in this paper lie in an area which 
had been especially studied by the author for some years back, and had led him to 
conclusions similar to some of those recently announced as the result of studies in 
north-western Scotland, which have justly attracted widespread attention. 
1. A zone of ancient crystalline rocks extends across south-eastern Pennsyl- 
yania, near Philadelphia, which is generally believed to underlie the lowest 
Cambrian strata and to be of Archeanage. ‘This zone is about a mile wide where 
it crosses the Schuylkill river, south of Conshohocken, and it is from this point to 
Westchester, some 20 miles westward, that the present remarks especially apply. 
Although in many portions exhibiting a distinct gneissic lamination, the rocks of 
this zone are held by the author to be of purely eruptive origin, consisting of 
syenites, acid gabbros, trap granulites, and other igneous rocks, often highly meta- 
morphosed. It is the outer peripheral portion of this zone to which attention is 
here directed. 
While the rocks are massive in the centre, this outer portion has been enor- 
mously compressed, folded and faulted, with the result of producing a tough, 
banded, porphyritic fucion gneiss, identical with the ‘milonite’ of Lapworth or 
the ‘sheared gneiss’ of Peach and Horne. So perfect is the fluxion structure 
that the rock resembles a rhyolite. As in the ‘banded granulite’ of Lehmann, 
elongated felspar ‘eyes’ Jie in flowing streams of biotite grains and broken 
quartz, the streams often parting and again meeting around the porphyritic ‘ eyes.’ 
Occasional crystalline eyes of hornblende remain, but most of it has been converted 
into biotite. 
A point of especial interest is that the felspar of the ‘eyes’ is quite colour- 
less and free from inclusions, like the sanidine of recent lavas; while on the other 
hand the felspars of the inner and massive portions of the zone, out of which this 
outer portion has been reformed by pressure fluxion, are full of inclusions and have 
the ‘dusty’ appearance so common in ancient felspars. The fresh-looking :fel- 
spar eyes have therefore very possibly been subsequently formed as the result of 
a recrystallisation of the old material under the influence of pressure fluvion. In 
similar manner the biotite has been made out of the old hornblende, garnets have 
been developed, and the quartz has been granulated and optically distorted by 
pressure. 
The influence of pressure is also seen in certain Cambrian strata in the immediate 
vicinity, where a sandstone containing cylindrical casts of Scolithus linearis, 
