SUMMARIES OF PRE-CAMBRIAN LITERATURE OF 



NORTH AMERICA FOR 1909, 1910, 191 1, AND 



PART OF 19 1 2 



EDWARD STEIDTMANN 



University of Wisconsin 



IV. ONTARIO, NORTHWEST TERRITORIES, AND THE EAST COAST OF 



HUDSON BAY 



Allen^ states that the Woman River area in the Sudbury Mining 

 Division of Ontario, west of Rush Lake, shows the following 



succession: 



Basic igneous dikes 1 .„ , . 



, ) Relative ages not known 



Mica porphyry J 



Acid igneous rocks — extrusive and intrusive 



Iron formation 



Basal greenstones 



The series has been intensely folded and extensively brecciated. 

 The strike of the iron formation banding is N. 45° E., but is in some 

 places at right angles to this direction where modified by cross- 

 folding. Everywhere the rocks stand practically on edge. The 

 basal greenstones and the iron formation are intruded by a great 

 many basic and acid dikes, the latter showing gradation into an 

 acid volcanic breccia overlying the iron formation. 



The various phases of the iron formation are: (i) finely banded 

 cherty carbonates, (2) hematitic, magnetic, pyritic, cherts, (3) black 

 and red jaspiHtes, (4) a unique amphibole-magnetite rock, in which 

 the petrographic character of the amphibole suggests riebeckite, 

 and (5) iron ore. The cherty iron carbonates are regarded as the 

 source of the other iron-bearing rocks, although the possibiHty that 

 some of the varieties may be partly original is not denied. The 

 derivation of the secondary varieties is ascribed to the same kata- 

 morphic and anamorphic processes by which Van Hise has explained 

 the origin of similar derivatives in the other iron formations. 



' R. C. Allen, "Iron Formation of Woman River Area " Eighteenth Annual Report 

 of the Bureau of Mines, 1909, Ontario. 



461 



