EESUMfi OF LITERATURE. 127 



Comments. — The members of the United States Geological Survey who 

 have been studying this area place the dividing lines in some cases at places 

 somewhat different from those where Grrant places them. They make the 

 same main divisions, however. The glauconitic greensand of Grant is now 

 known not to contain potassium, the green granules being composed of a 

 hydrous ferrous silicate." 



The United States geologists concur in the general conclusions reached 

 by Grant as to the character and cause of the metamorphism. 



1901. 



WiNCHELL, N. H. The geology of Minnesota: Final Report Geol. and Nat. 

 Hist. Survey of Minn., Vol. VI, 1901. Geological atlas with synoptical descriptions, 

 88 plates. 



This is a collection of maps of Minnesota. The earlier ones, froin 

 Franquelin's map of 1688 up to and including Nicollet's of 1842, are repro- 

 duced, and then the later maps published by the Geological and Natural 

 History Survey in the reports preceding this. Brief explanatory notes 

 accompany each plate. 



WiNCHELL, N. H. Glacial lakes of Minnesota: Bull. Geol. Soc. Am., Vol. XII, 

 1901, pp. 109-128, pi. 12. 



Winchell gives a brief description of a number of glacial lakes occur- 

 ring in Minnesota. Among these there are two, Lake Norwood and Lake 

 Onnamani, which lie partially or wholly in the Vermilion district. 



Van Hise, C. R. The iron-ore deposits of the Lake Superior region: Twenty- 

 first Ann. Rept. U. S. Geol. Survey, Pt. Ill, 1901, pp. 305-431:, 12 plates, 6 of 

 which are geological maps. 



This paper contains a brief description and comparison of the various 

 iron-bearing districts of the Lake Superior region. 



The first chapter contains a general discussion of principles. The 

 rocks of the region, disregarding the late formations, are stated to be divisible 

 into the following five series, enumerated from base up : Archeau, Lower 

 Huronian, Upper Huroinan, Keweenawan, and Cambrian. 



The chief varieties of the iron-bearing rocks and their alterations are 

 described. They are shown to occur in the three series, the Archean, Lower 



"The Mesabi iron-bearing district of Minnesota, by 0. K. Leith: Mon. U. S. Geol. Survey Vol. 

 XLIII, 1903, pp. 110. 



