Reviews. 



SUMMARIES OF PRE-CAMBRIAN LITERATURE FOR 1902-1903. II. 



[Continued from J>. 02.'] 



C. K. Leith. 

 A. P. Coleman and A. B. Willmott. " The Michipicoten Iron Ranges." 

 "Geological Series," Utiiversity of Toronto Studies, 1902, pp. 39-83. 

 See also Report of the Bureau of Mines, Ontario, 1902, pp. 128-51. 

 Coleman and Willmott describe and map the Michipicoten iron ranges. The 

 rocks are classified as follows : 



["Laurentian Gneisses and granites 



I Basic eruptives 



Upper Huronian -j Acid eruptives 



1^ Dord conglomerate 



Arch^an 



^ 



Lower Huronian 



Eleanor slates 

 Helen iron formation 

 Wawa tuffs 

 Gros Cap greenstones 



I 



The Gros Cap greenstones are basic eruptives with ellipsoidal structure corre- 

 sponding in position and character to the Ely greenstones of the basement complex of 

 the Vermilion district of Minnesota. They are in part basal to the other rocks of 

 the district, but in part also they are interbedded with the rocks of the Helen iron 

 formation. The Wawa tuffs are acid schists having the composition of quartz- 

 porphyry or felsite, usually in the form of tuff, ash, or breccia, and sometimes show 

 stratification, taken to indicate deposition by water. 



Slates of distinctly sedimentary origin, occurring in thin bands near Eleanor Lake 

 and called the Eleanor slates, are referred to the Lower Huronian. Their relations to 

 the Helen iron formation are not known. 



The Helen iron formation, 500 feet thick, comprises banded granular silica with 

 more or less iron ore, black slate, siderite with varying amounts of silica, and griinerite 

 schist. All are found well developed at the Helen mine, and all but the griinerite schist 

 have been found in the Lake Eleanor iron range also, while granular silica and siderite 

 occur in large quantities in every important part of the range, though small outcrops 

 sometimes show the silica alone. All of the rocks of the iron formation contain con- 

 siderable amounts of iron pyrites. The grained silica and the granular silica is similar 

 in certain respects to the jaspers and ferruginous cherts of the United States, and their 

 origin is believed to be the same. They differ in being often soft, pulverulent, and 

 brecciated. The black, graphitic slate, forming a thin sheet just under the iron 

 range proper west of the Helen mine and at other points in the region, seems closely 

 related to the granular silica, being composed of the same material with a large 

 admixture of carbon which smears the fingers. 



Iron ore is mined in the Helen mine, and this mine is described in detail. The 



161 



