416 PROCEEDINGS OF SECTION C. 
micaceous gneisses of the other appear as a passage from the 
sediments to the igneous rocks. In Green Wattle Creek and at 
Wilson’s Creek the two classes of schists are seen separated. At 
Dargo River and at Marengo where the two sets are in contact 
metamorphism has taken place, thus masking the true character. 
It may be accepted as a preliminary distinction that where 
felspars occur in the schists, and more especially where they are 
surrounded by detritus and form “eyes” in the foliations, the 
original rock was plutonic ; but when the rocks have no felspar, 
but are composed of merely mica and quartz, the original rock 
was a sediment. Yet these distinctions are not hard and fast, 
for the complete comminution of a plutonic rock might give rise 
to a regenerated schist composed of biotite, mica and quartz. 
One of the most suggestive observations which I have now made 
is that the quartz of these schists has been far more plastic 
than the felspars. Why silica should be so rather than a silicate 
of alumina and alkali, which is less refractory to high temperature, 
T do not at present see. But this is certain, that the quartz has 
been drawn out and bent, while the felspar has been broken. 
It may be that the action has not been merely that the 
constituent minerals of the rock have become free to re-arrange 
themselves by reason of the enormous pressure to which they 
have been subjected. It has seemed to me that solutions must be 
taken into account. Yet the rock itself has not gone into solution 
for the felspars remain intact excepting in so far that mechanical 
action has broken them. 
So little, however, is yet known of the behaviour of mineral 
substances under great pressure that it is but wise to refrain 
from endeavouring to explain those phenomena which present 
themselves as exceptional. 
My results so far seem to me to support the views enunciated 
by Professor Lehmann as to dynamo-metamorphism, at p. 33 of 
his great work on the Crystalline Schists of Saxony. (Alt krystal- 
linischen Schiefergesteine. Bonn, 1884). 
Put shortly, they are these :—Rocks which by reason of great 
earth-stress, not only assume new forms of structure, but also 
are compelled to adapt themselves to a less space and eliminate 
constituent substances. Most energetic re-combinations of sub- 
stance accompany the deep-seated crushing of rock, and any open 
fissures become filled with secretions. This can, however, only 
take place under such superincumbent weight as will suttice to 
prevent an actual disruption of the rock, and such phenomena 
are usually only apparent in the heart of mountain chains. Such 
secretions can only exude when the pressure in the rocks exceeds 
the limit of plasticity, and there is a want of compensating 
counter pressure which causes the disruption of the whole system 
of beds. Lehmann believes that it is at such a time that the 
granite magmas enter the fissures and mix with the secretions 
of the metamorphosed rocks. 
