82 ROYAL SOCIETY OF CANADA 



more or less associated with tliem, and of a remarkable glacial deposit 

 overlying them. The red jasper is closel}^ like our own, and brown 

 banded specimens are like some phases of the Helen Iron Formation, 

 bnt a black finely laminated specimen is of a different type from any 

 Canadian example. A piece of brown jasper is indistinguishable from 

 specimens obtained at the Helen mine. 



The splendid brown- or dark green crocidolite, with its beautiful 

 silky lustre, associated with the lower part of the rocks containing 

 banded iron ore is not at all matched in appearance by the dark green 

 hornblende, griinerite, associated with magnetite in our own iron ranges. 

 The composition of the asbestos and of the griinerite is, however, quite 

 similar, each consisting largely of silica and ferrous exide. The croci- 

 dolite (according to Dana) contains, however, much ferric oxide and 

 a little soda also. 



Rogers mentions oolitic rocks associated with the banded iron bear- 

 ing series, suggesting the oolitic jaspers of our Animikie, though 

 very different in appearance. Oolitic jasper has never been re- 

 ported from the more ancient Keewatin Iron Formation of America, 

 but only from the Upper Huronian iron bearing rocks. In some places 

 the Griqua Town beds containing the banded silica and iron ore are much 

 folded, and they often rise as isolated patches above the general surface 

 of granite and gneiss, apparently much as our own iron ranges do in 

 parts of northern Ontario. In other places, however, they overlie 

 conformably limestones and other rocks of the Campbell Rand group, 

 and lie nearly flat. In Ontario the Iron Formation has been found 

 associated with crystalline limestone only in one place, Goudreau lake, 

 north of Lake Superior; and is usually more nearly vertical than hori- 

 zontal in attitude. 



In his latest publication ^ Rogers describes curious breccias of large 

 and small fragments of banded jaspery rocks and cherts with a matrix 

 of hematite or silica or a mixture of the two. " In places the rock 

 appears to be made of little else than hematite, and when broken open 

 faint outlines of angular fragments of banded rock, now converted into 

 hematite, can be seen embedded in a matrix of hematite." This descrip- 

 tion would apply very well to some of our ore deposits, as at Helen 

 mine, where a breccia of the Iron Formation has been transformed into 

 lean ore. 



The age of these South African iron bearing rocks, so similar to 

 our American Iron Formation in structure, chemical composition and 

 relationship to adjoining rocks, is not very certainly determined. There 



* Campbell Rand and Griqua Town Series in Hay, Trans. Geol. Soc. of 

 South Africa. 



