REVIEWS 283 



composition, and their monotonous character, in this respect, has been 

 frequently commented upon. 



Brecciation, which is so frequently characteristic of these deposits, is 

 an almost constant feature of eruptive contacts, resulting from the detaching 

 of material from the containing walls. 



This conclusion is in accord also with evidence drawn from analogy 

 with chemical and metallurgical principles. 



Dr. Barlow concludes further that there can be little doubt of the 

 abundant presence of heated solutions and vapors, which were capable 

 of dissolving out, and, under certain conditions, redepositing these 

 sulphides. Such agencies certainly began their work before the whole 

 magma had cooled, bearing their heavy burdens of sulphide material, most 

 of which was obtained from the magma in the immediate vicinity,to occupy 

 the various cavities and fissures as fast as these were formed. The whole 

 of this action was practically completed before the intrusion of the later 

 dikes of the olivine-diabase, which are now regarded by Dr. Barlow as the 

 end product of the vulcanism to which the norite masses owe their intrusion. 

 In certain of the deposits the various hydrochemical agencies accom- 

 panying dynamic action have been more active than in others, as at the 

 Victoria mine, and some of the Copper Cliff mines, but in others — as, for 

 instance, the Creighton mine — magmatic differentiation has been the main 

 and almost sole principle determining and favoring the development of 

 this, the largest and richest sulphide nickel mine in the world. 



The evidence summarized by Dr. Barlow seems to show beyond reason- 

 able doubt that the norite is the original source of these sulphides. How- 

 ever, he describes evidence of redistribution by aqueous and gaseous 

 solutions accompanying later stages of the norite eruption, and it is difficult 

 to see how this evidence will enable one to draw any line between, or deter- 

 mine relative emphasis to be placed on, redistribution by such agencies 

 and redistribution by meteoric waters heated by contact with the cooling 

 norite or by meteoric waters acting subsequent to its cooling. Differ- 

 ence in emphasis on these factors now constitutes the main outstand- 

 ing difference of opinion as to the origin of the ores. 



The report is accompanied by a brief description of the geology of well- 

 known nickel deposits of the world, and a summary of the metallurgical 

 principles applicable to the extraction of nickel, making it useful as a 

 nickel handbook. All interested in the geology of ore deposits will appre- 

 ciate Dr. Barlow's adequate and satisfactory treatment of his subject. 



Reference should be made to two other reports on the district which 

 have appeared in the last two years — one by Mr. Charles W. Dickson, in 



