i7 



begin with a green band of hornblende on the outside, fol- 

 lowed by an intergrowth of long blades of hornblende with 

 white plagioclase. The latter on the inner side becomes 

 coarse " graphic granite " with interleaved quartz, and the 

 centre of the mass may consist of almost pure quartz. The 

 largest example of the kind, a mile south of Copper Cliff, 

 was worked as a quartz mine, and furnished thousands of 

 tons of fairly pure quartz used as flux at the smelter, lr 

 seems most probable that the coarse textured rock surround- 



Structure in Gabbro, Sudbury. 



ing the quartz is a sort of " reaction rim " about a partially 

 digested block of quartzite. A little pyrrhotite containing 

 some nickel occurs with these masses of quartz suggesting 

 a relationship to the nickel-bearing eruptive a few miles 

 to the northwest. 



The sedimentary rocks of the Sudbury series mentioned 

 above were tilted and folded and penetrated by eruptives, 

 and then carved down to an uneven plain before the Huron- 

 ian began. On the upturned edges of the quartzite a coarse 



