k£sum£ of literature. 95 



In the above papers N. H. and H. V. Winchell maintain that the iron 

 ores of the Keewatin of Minnesota are not derived from a carbonate, but 

 are probably a direct chemical precipitate; for there is no evidence of the 

 existence of carbonate of iron at any time, and the nature of the country 

 rock is such as to imply that no carbonates in amounts required could have 

 been deposited at the time the rocks were formed. 



Winchell, Alexander. Some results of Archfeaii studies: Bull. Geol. Soc. 

 Am., Vol. I, 1890, pp. 357-394. 



Alexander Winchell in 1890 repeats his general conclusions as to the 

 stratioTa]3hy in northeastern Minnesota already g-iven in his reports of field 

 work in the A^ermilion district for the years 1886 and 1887, and published 

 in the fifteenth and sixteenth annual reports of the Minnesota survey, pages 

 5-207 and pages 138-391. 



Summed up, these conclusions are briefly as follows: In northeastern 

 Minnesota there are large areas (in the Vermilion district four) of granitoid 

 and gneissoid rocks which have oval outlines trending in general northeast- 

 southwest. Gneissoid rocks predominate, and the rocks approaching a 

 granitoid condition are found only at the centers of the areas. These 

 gneissoid areas are surrounded by crystalline schists, mica-schists, hornblende- 

 schists, or mica-hoi"nblende-schists, known as the Vermilion series. These 

 strike east-northeast. The dip increases away from the granitoid areas 

 until it becomes vertical. The gneissoid (granitoid) rocks and schists are 

 intimately connected, and the author, while declining to make a definite 

 statement, clearly intimates that the gneiss, granites, and schists are all of 

 sedimentary origin. Referring to those rocks, he says: 



They are so inseparable on any fundamental g-rounds, and are so blended together, 

 both structurally and mineralogically, that no reasons appear to exist for a reference 

 of one class to a mode of origin fundamentally different from the mode of origin of 

 the other class. On this question, however, I only propose at present to cite some 

 observed facts. The interpretation of them may be subsequent!}' undertaken. 



The crystalline schists are succeeded bv a system of semicrystalline schists [the 

 Keewatin]. The}' range, however, from fragmental crystalline to earthy. They 

 succeed in perfect structural conformity with the older schists, with onh' slight indi- 

 cations of stratigraphic disturbance. Their attitude is generally vertical or steeply 

 inclined. Their position is between and surrounding the gneissoid areas [p. 377]. 



In the Vermilion district, as they lie between two elongated gneissoid 

 areas, they have a persistent east-northeast strike for 70 miles. In each of 



