T. B. Brooks— Youngest Huronu 



The approximate conformability in strike and dip of the Hu- 

 ronian and Copper series, observed by Prof. Pumpel]jand my- 

 self between the Montreal Eiver and Lake Gogebic,* would, in 

 this view, be only accidental and not prove identity of age, as 

 we were at the time inclined to suppose, and with which view 

 Mr. Irving agreed. 



As supporting the view that these pre-Silurian systems f are 

 of distinct periods, I would call attention to their well-known 

 points of difference The Huronian series of stratified green- 

 stones, chloritic and related schists, clay slates, quartzytes, mar- 

 bles, micaceous and hornblende schists, gneisses and granites, 

 containing no copper or other metallic ores, except great con- 

 formable beds of magnetite, hematite, and limonite, differ as 

 widely as may be from the compact and amygdaloidal mela- 

 phyres, friable sandstones, conglomerates with porphyry pebbles, 

 which constitute the bulk of the Copper series, the whole more 

 or less charged with native copper and silver; all of which 

 points strongly toward a different origin for the two systems. 

 In their metamorphoses and movements subsequent to their 

 deposition, there is a not less wide divergence noticeable. The 

 friable sandstones of the Copper series, showing no greater met- 

 amorphism than the overlying Silurian for which they are often 

 mistaken, has no counterpart in the highly crystalline schists 

 and quartzytes of the Huronian, where we have only just 

 enough of the arenaceous character left in some of them, to leave 

 no doubt as to their fragmentary origin. But the difference in 

 the amount, sharpness, and regularity of the folding and bend- 

 ing of the rocks of two systems into existing wave-forms, 

 IS if possible wider than their lithological variations. Contrast 

 the magnificent regular sweeps of the Copper series, the main 

 ranges of which preserve the same strike and direction of dip 

 from Keweenaw Point westward for 150 miles, presenting for 

 naif the distance only the south upturned edge of the broad 

 synclinal which embraces one fourth of the great lake in its 

 basin;:}: with the older system, everywhere sharply folded 

 into narrow troughs and irregular basins, trending in every di- 

 rection, the upturned edges of whose enclosing rocks box the 

 compass, winding and zig-zaging in outcrop like a sluggish 

 river. § 

 * This Jour., vol. iii, June. 1872. 



[ity and difierence in age of the Copper-bearing 

 3f Lake Superior, as established by the facts re- 

 tnpeUy and my.self and of Mr. Irving,^in this Jour- 



i depression which ceased at the begini 



t See Irving's^int 

 § Dr. J. P. Kimbi 



