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The nickel and copper are confined to the norite and its altered vari- 

 eties. Closely associated with this is a rock of granitic composition of 

 prevailing gneissoid texture, which cannot be sharply separated from the 

 basic eruptive, although the change is usually sharp enough to allow of 

 a boundary being drawn between them. The norite ranges, as shown by 

 Coleman, are probably the exposed portions of one continuous laccolite, 

 with occasional minor irregularities or offsets, which has been folded into 

 a platter-shaped trough, holding in its depressed interior nearly flat-lying 

 Huronian (?) sediments constituting the uppermost series of the district. 

 The relations of these sedimentary rocks to the norite are in doubt, but 

 later work seems to indicate a close relationship, both in origin and age, 

 with the main masses of norite. 



The nickel is mainly in the form as a nickel iron sulphite, pentlandite, 

 associated with pyrrhotite and chalcopyrite. That the ore has been 

 segregated more or less directly from magma is believed to be shown by 

 the following facts : 



The deposits, without exception, all occur at the margin of the gabbro 

 or norite, the rock itself in immediate association with the ore being finer 

 in texture, and relatively much more basic in composition, than portions 

 further removed from the contact. 



The sulphides are always much more sharply defined against the walls 

 of the intrusion than on the inner side towards the main mass of the gabbro. 



These deposits are always found in such intimate association with the 

 norite or hypersthene gabbro. 



Pyrrhotite, chalcopyrite, and pyrites are all ordinary constituent min- 

 erals of the normal norite, and are, at times, comparatively abundant even 

 in exposures situated some distance from the contact. 



The sulphides are, undoubtedly, of primary origin, and are among 

 the earliest of the minerals to crystallize out from the original magma, 

 sometimes even antedating the iron ore, in which they are occasionally 

 completely inclosed. 



The transitional type between the normal norite and the richer forms 

 of the pyrrhotite-norite furnishes unmistakable evidence that in these cases, 

 at least, the sulphides were formed during the cooling and crystallization 

 of the norite magma, and that they were very little affected by any secondary 

 action. 



Secondary quartz, calcite, and dolomite are occasionally present, in 

 appreciable amounts, but the prevailing scarcity of these minerals at most 

 of the deposits has always been a subject of remark. 



The deposits are singularly uniform in chemical and mineralogical 



