26 



pyroxene and a few large bits of biotite, One finds also a 

 little interstitial quartz and a few distinct blebs of bluish 

 quartz. The most basic phase of the rock analysed con- 

 tains about 50 per cent, of silica, and the most acid example 

 of mieropegmatite about 69 per cent., showing a consider- 

 able range from the bottom of the sheet to the top. 



All the rocks of the district are cut by dikes of very fresh 

 olivine diabase, some of which are 200 or 300 feet wide, 

 and may be traced, as shown by Dr. Barlow, for seven 

 miles, passing through norite, ore and country rocks impar- 

 tially. This diabase and some dikes and irregular masses 

 of granite are the youngest rocks of the region and may date 

 from early Paleozoic times. 



THE NICKEL DEPOSITS. 



The nickel ores which give economic importance to the 

 region are of a very uniform and monotonous character. 

 In all the larger mines the ore consists of pyrrhotite in 

 largest amount with subordinate quantities of pentlandite, 

 (NiFe)S, and chalcopyrite. The pentlandite may be finely 

 disseminated through the pyrrhotite and not apparent to the 

 eye, but polished surfaces of the ore, as shown by Campbell 

 and Knight, prove its presence under the microscope. The 

 ore always contains small quantities of the norite minerals 

 and sometimes fragments of norite or country rock. The 

 country rock may be any of the older formations, sediments 

 of the Sudbury series, acid or basic eruptives, or Laurentian 

 gneiss, without in anyway affecting the ore deposit; but no 

 ore deposit has yet been found without norite. " No norite, 

 no ore," is the law of the district. There are, however, 

 long stretches of the norite edge where no ore occurs, where 

 the sheet is unusually narrow, or where the country rock 

 bends inwards instead of outwards. There are cases where 

 the norite edge is gossan covered continuously for more 

 than a mile, as in the vicinity of the Murray mine. 



The ore bodies may be divided into two principal kinds, 

 marginal deposits, at low points or bays on the edge of the 

 norite ; and offset deposits, where channels lead out from 

 such bays conveying the ore mixed with norite to various 

 distances from the edge, sometimes even three or four miles 



