380 MR. A. M. FINLAYSON ON THE NEPHRITE [Aug. I909, 



Fig. 5. Antigorite-rock : Griffin Range (Westland). The antigorite occurs 

 as long interlacing needles penetrating the partly transformed augite, 

 which is seen in the centre. (See p. 360.) 

 6. Olivine-gabbro: locality doubtful. The pyroxene is altered to 

 bastite (black). The mottled portions consist of olivine grains 

 undergoing a change into fibrous amphibole round their margins. 

 (See p. 374.) 



Discussion. 



The Secretary read the following remarks, contributed by 

 Prof. T. G. Bonnet : — 



'I very much regret that, owing to a short absence from Cambridge, I did 

 not know that this paper would deal with the interesting rocks from the West- 

 land district of New Zealand, or I would have arranged to stay for the night. 

 Thanks to the kindness of Dr. Bell, I have had the opportunity of examining 

 some of the specimens, and can see that the paper will be a very valuable 

 addition to our knowledge of these interesting and often remarkable magnesian 

 rocks. Had I been able to join in the debate, I should have ventured to 

 suggest the possibility of the talc-rock and the magnesite being the result 

 of the action of great, pressure on the serpentine and the bowenite— -that 

 is, precisely the reverse of the process suggested by the Author ; for, so far as 

 my experience has gone, a talc-rock is the condition to which a much-crushed 

 serpentine is reduced (see instances on the Gorner Grat, near Zinal, and at Plas 

 Goch, Anglesey). Also, in regard to the nephrite, I would suggest that the 

 direct transformation of olivine into any form of actinolite seems a difficult 

 matter ; for the former mineral contains practically no lime, the latter a con- 

 siderable percentage. Must not this constituent (and some silica) be accounted 

 for? Also I would ask, as above, in regard to the fourth mode: Is it not 

 more likely that the serpentine-talc-carbonate rock is a further stage of change 

 in the nephrite ? 



Mr. E. D. Isaacson said that it was with great pleasure that he 

 had listened to the very able paper which they had just heard ; 

 the large amount of work put into it, both in the field and in the 

 laboratory, was also worthy of great commendation, the former 

 often carried out under great difficulties. As had been pointed 

 out, these magnesian rocks were of wide distribution, and the 

 speaker had personally been deeply interested in. the metamorphism, 

 especially the Dun-Mountain types. From his own observation, he 

 could heartily endorse the Author's remarks, and during the course 

 of a long residence on the Dun Mountain observed nothing to cause 

 him (the speaker) to traverse the Author's statements. 



Mr. A. R. Andrew congratulated the Author on the success of 

 his paper, the preparation of which had clearly entailed a vast 

 amount of labour and time, both in the laboratory and in the 

 snow-clad fields which had been depicted on the screen. He 

 enquired on what grounds the Author had ascribed the intrusion 

 of these ultrabasie rocks to so late a period as the Cretaceous. 



Mr. J. V. Elsden remarked upon the alteration of olivine into 

 amphibole, which required the presence of lime. He would 

 suggest the possibility that, in this case, the olivine might not be 

 pure forsterite, but a lime-bearing species, perhaps of the monti- 

 cellite type. 



