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Thin sections of these rocks show the same polygonal shapes of the 

 grains of quartz, and more or less iron ore is associated with speci- 

 mens from each locality. It is very probable, then, that the same 

 horizon exists at points far to the west of Lake Superior. 



Turning toward the east, specimens very like the jaspery varieties 

 of the Michipicoten iron range are found interbedded with iron ores 

 near Lakes Wahnapitae and Temagami, between Sudbury and the 

 Ottawa River. 



At Batchawana Bay at the southeast end of Lake Superior, a 

 siliceous rock with narrow bands of magnetite occurs, which is prob- 

 ably the equivalent of the Michipicoten rock. 



If, as seems probable, these jaspers are the equivalents of the west- 

 ern Huronian sandstones, there is a definite horizon traceable from 

 point to point across the whole northern end of the province, a dis- 

 tance of more than six hundred miles. 



At a number of places over this area conglomerates, containing 

 jasper, ferruginous sandstone or chert pebbles, probably derived from 

 the source above described, are known. Beginning at the west, some 

 of these conglomerates occur, as follows : on Shoal Lake, east of Rainy 

 Lake ; west end of Schist Lake; near Mosher Bay, at the east end of 

 Upper Manitou Lake ; a mile east of Fort Frances on the Rainy 

 River; near Rat Portage; near the mouth of Dore River; in the 

 original Huronian area, north of Lake Huron, particularly the Thes- 

 salon area; on Lake Temiscaming. 



It is assumed that the iron-formation material cannot be other 

 than Lower Huronian, and that the conglomerates must represent a 

 basal horizon of the Upper Huronian. The break between the Upper 

 and Lower Huronian thus represented is a most profound one, and 

 affords a good basis for the correlation of the Huronian formations. It is 

 further suggested that this great unconformity maybe the same as 

 that between the Upper and Lower Huronian formations on the south 

 shore of Lake Superior and in Minnesota. 



Comment. — As stated by Dr. Coleman a number of the conglomer- 

 ates above mentioned have been regarded by Pumpelly, Irving, Van Hise, 

 and other United States geologists, as basal to the Lower Huronian — on 

 structural evidence. Dr. Coleman places them in the Upper Huronian 

 because they contain fragments of iron formation material which 

 are assumed to be Lower Huronian. According to the generally 

 accepted ideas of the number and relations of the pre-Cambrian 



