130 R. BELL NICKEL AND COPPER DEPOSITS OF SUDBURY. 



those two and running parallel with them, is found in the northeasteni part 

 of the township of Morgan. 



The next member of the series, in ascending order, is the most remarkable 

 of all. It consists of a thick belt of nearly black volcanic breccia, which 

 has been traced from Vermilion lake northeastward in the valley of Ver- 

 milion river to beyond the latitude of Wahnapitse lake. It is a compact 

 silicious rock, with conchoidal fracture and consists of angular fragments, 

 mostly small, closely crowded together and flecked with irregular angular 

 white spots. These Dr. G. H. Williams finds to consist of fragments of 

 pumice, which, while retaining their structure, are completely replaced by 

 silica. This band appears to be several thousand feet thick and, as it has 

 resisted denudation well, forms an elevated, rough and broken country 

 along its whole extent. 



The highest rocks of the series in this district, or those which occupy the 

 center of the trough, are made up of evenly bedded drab and gray argilla- 

 ceous sandstones or graywackes, interstratified with shaly or slaty belts, and 

 overlain at the summit by black slates. As these rocks dip at comparatively 

 low angles, they occupy a greater geographical width than the other mem- 

 bers in proportion to their thickness, which, however, must be very consid- 

 erable. 



Along the lower part of Spanish river, above and below the great bend, the 

 Huronian belt has a wider spread than near Sudbury Junction and here we 

 find a considerable development of rocks associated with the quartzites which 

 are not met with to the northeastward in the district under consideration. 

 Among these are, soft bluish-gray satiny sericitic schist, sometimes ligniform, 

 accompanied by nearly black hornblendic schist ; coarse and fine-grained 

 glossy green and greenish -gray schist ; silver-gray fine-grained mica-schist, 

 studded with crystals of staurolite ; hard green schist ; dark-gray clay-slate; 

 fine-grained greenish-gray silicious felsite ; and slaty gray wacke, passing 

 into gneiss. 



The stratified Huronian rocks and also the gneiss and quartz-syenite of 

 Sudbury district are traversed by dikes of gray, coarsely crystalline diabase, 

 which are often large and can be traced for considerable distances. Their 

 commonest course is about west-northwest. They all have the same physical 

 characters and appear to be of identical composition. The sound, fresh rock 

 is extremely tough, but the exposed surfaces disintegrate easily under the 

 weather into brown crumbling debris, especially along the joint-planes and 

 at their angles. The outer portions of the masses thus separated scale off 

 concentrically, so that they become rounded and bowlder-like. These dikes, 

 as we shall show further on, apparently play an important part in the 

 economic geology of the district. 



