Vol. 65.] AND MAGNESUN ROCKS OF NEW ZEALAND. 381 



Prof. "Watts said that it was evident that the Author had devoted 

 much work in the field and in the laboratory to the paper, and 

 thought that he deserved great credit for his presentation of new 

 and difficult matter. He had not shrunk from a bold explanation 

 of the origin of the nephrite ; and it would remain for the future 

 to demonstrate whether his inference was justified by the facts, 

 or whether the difficulties suggested by Prof. Bonney were so 

 considerable as to forbid the adoption of the Author's explanation. 



The Author, in his reply, thanked the Fellows for their com- 

 plimentary references to his paper. With regard to the points 

 raised, the association of bowenite and of nephrite with talcose 

 rocks seemed in this case due to a derivation of both the talc and 

 its contained mineral from a pre-existing peridotite-mass by 

 dynamic processes. In reply to Prof. Bonney, the Author said 

 that the evidence showed that the bowenite and nephrite, rather 

 than the talc-rocks, were associated with effects of rock-pressure. 

 There was no evidence of further alteration of the nephrite by 

 crushing, and he concluded that the nephrite was an end-product 

 of intense pressure and movement. The source of the lime in the 

 alteration of olivine to nephrite was an obvious difficulty, on which 

 light would probably be thrown when the rock was studied in its 

 field-relations. The olivine might possibly be monticellite, although 

 the olivines of these peridotites were not, so far as he had examined 

 them, lime-bearing varieties. In any case, the change to nephrite 

 was here a direct alteration, there being no trace of intermediate 

 products such as serpentine. The evidence as to the age of the 

 intrusions was more or less arbitrary, and rested on the assumption 

 that the period of uplift of the rocks of the Alpine range was late 

 Mesozoic. He was indebted, for some of the specimens of nephrite 

 exhibited, to Mr. Prank Hyams, of Bond Street, one of the pioneer 

 collectors of the mineral. 



I J. G. S. No. 259. 2 c* 



