284 Reports and Proceedings — 



The authors, after re- examination of a large number of sections, 

 feel no doubt of the accuracy of their original view that the peridotite 

 was intruded into the hornblende schists and banded "granulitic" 

 rocks, after these had assumed their present condition. In it they 

 find no signs of any marked pressure-metamorphism, either prior or 

 posterior to serpentinization. They have failed to connect the 

 streaky or banded structure with any foliation or possible pressure- 

 structure in the schists, and they can only explain it as a kind of 

 fluxion- structure, viz. as due to an imperfect blending of two magmas 

 of slightljr different chemical composition, anterior to the crystal- 

 lization of the mass. 



The Porthalla sections have been examined with especial care, not 

 only because the serpentine is nowhere so conspicuously banded, but 

 also because its intrusive character has been denied, both it and the 

 hornblende schists being ascribed to the alteration of a series of 

 sedimentary rocks of suitable composition. For this view the 

 authors have failed to discover any evidence, and consider it 

 contrary to stratigraphical and petrographical facts. 



In regard to the genesis of the ci'ystalline schists, which for pur- 

 poses of reference were divided by Prof. Bonney into a "granulitic," 

 a " hornblendic," and a " micaceous " group, the authors show that in 

 parts of the first the more acid rock breaks through the more basic, 

 as if intrusive, in others they appear to be perfectly interstratified, 

 the one passing backwards and forwards, though rapidly, into the 

 other. But between these extremes, intervals can be found where 

 the two rocks seem as if partially drawn out together. The authors 

 are agreed that certainly one, probably both, of these rocks are 

 igneous, that when the basic rock was solid enough to be ruptured, 

 the acid magma broke into it, and sometimes softened it sufficiently 

 to allow of the two flowing for some little distance together, after 

 which crystallization took place. In regard to the hornblende schists, 

 the authors are not yet satisfied that either fluxion or mechanical 

 crushing will account for every structure which they have exaaiined, 

 and prefer to leave the question, in certain cases, an open one. The 

 most distinctive features of the micaceous group appear due to sub- 

 sequent earth-movements, so that, though it exhibits some special 

 characteristics, the authors are doubtful whether it is any longer 

 worth while separating it from the hornblende schists. 



Of the igneous rocks newer than the serpentine, the gabbro has 

 received the closest attention. It exhibits in places (especially in 

 the great dj'ke-like mass as Carrick Luz) a very remarkable foliation 

 or even mineral banding, which has been claimed as a result of 

 dynamo-metamorphism. The authors bring forward a number of 

 instances to establish the following conclusions : — (a) That this 

 foliation occurs most markedly where the adjacent serpentine does 

 not show the slightest sign of mechanical disturbance ; (h) that it 

 must be a structure anterior to the consolidation of the rock ; (c) that 

 it sets in and out in a very irregular manner; {d) that when it was 

 produced the rock was probably not a perfect fluid. Hence they 

 explain it also as a kind of fluxion structure, produced by differential 



