172 REVIEWS 



represent the Archaean. The Lower Huronian and Archaean of the present report 

 correspond approximately with the Upper and Lower Keewatin of the Minnesota Sur- 

 vey, although there are minor differences in the reference of the several geological 

 units to these divisions. 



In the Mesabi district the rocks underlying the Animikie of the Upper Huronian 

 had previously been lumped together as Archaean by the U. S. Geological Survey. 

 They are now shown to be divisible into (i) a sedimentary formation, referred, with its 

 associated intrusives, to the lower Huronian, showing remarkable similarity in lith- 

 ology and structure to the Lower Huronian of the Vermilion distiict; and (2) an 

 igneous series, referred to the Archaean, with marked similarity to the igneous rocks of 

 the Archaean of the Vermilion district. The Lower Huronian and Archaean thus cor- 

 respond roughly to the Upper and Lower Keewatfn of the Minnesota Survey. This 

 division of the Keewatin was not made in the Mesabi district by the Minnesota Geo- 

 logical Survey, although Dr. Grant noted the occurrence of rocks characteristic of the 

 two divisions, and suggested the possibility of their separation. 



The correlation of the Animikie series of the Vermilion and Mesabi districts with 

 the Upper Huronian series of the north shore of Lake Huron is the same as in previous 

 reports of the U. S. Geological Survey, and is the feature of the correlation which has 

 been severely criticised by Canadian and other geologists, including Coleman, Willmott, 

 Winchell, and Lawson, who hold the Animikie to be unconformably above the origi- 

 nal Huronian series of the north shore of Lake Huron, from which the term " Huron- 

 ian " comes. Comments on their arguments are made in connection with summaries 

 of their articles on a preceding page. 



The reference of the sedimentary Soudan iron formation to the Archaean, instead 

 of including it in the Huronian and thus making a threefold division of the Huronian, 

 as is now possible in the Marquette district, has also been criticised. The defense of 

 such a use of the term " Archaean " involves a discussion of the principles of pre-Cam- 

 brian nomenclature not here warranted. Such a discussion will be made in a final 

 monograph on Lake Superior geology now in preparation by the U. S. Geological 

 Survey. 



N. H. W^iNCHELL. Some Results of the Late Minnesota Geological Survey. 



Americafi Geologist, Vol. XXXII (1903), pp. 246-53. 



Winchell summarizes some results of the work of the late Minnesota Geological 

 Survey. Those referring to the pre-Cambrian are as follows (the numbers are Profes- 

 sor Winchell's) : 



5. The discrimination of two iron-bearing formations in northern Minnesota, thus 

 separating the Mesabi range stratigraphically from the Vermilion. This observation 

 was continued into Wisconsin and Michigan by a visit to those states, and the same 

 dualty was pointed out in the iron regions of those states, and was announced for the 

 first time in the Minnesota report for 1888. It has since been discovered that there is 

 still a third iron horizon in northeastern Minnesota, not mentioning the titanic iron 

 ore of the gabbro. It is the upper Keewatin, the others being in the Lower Keewatin 

 and the Taconic. 



6. The separation of the Archaean of Minnesota into two non-conformable parts, 

 viz., the Upper and Lower Keewatin, with a great basal conglomerate between them. 



7. The determination of the oldest known rock of the Lake Superior region, a 

 greenstone called Kawishiwin, the bottom rock of the Keewatin, the supposed earliest 

 crust of the globe. 



