RESUME OF LITERATURE. 103 



similar to that on the north shore of Lake Huron. This conglomerate is 

 not the same as the ag-glomerates of the Kewatin, such as that on Stuntz 

 Island, at Vermilion Lake, and Ely. The Kewatin is always nearly vertical, 

 while the dip of the Taconic rarely exceeds 15°. The iron-ore beds of the 

 Taconic are: (1) The quartzose, hornblendic (or olivinitic), magnetitic group 

 of the Pewabic quartzite; (2) an impure jaspilite, hematite, and limonite 

 group; (3) a carbonated iron group; (4) a gabbro titanic iron group. The 

 jaspilitic hematite group has the same lithologic peculiarities as the 

 jaspilite beds of the Vermilion range. The gabbro in which the titanic 

 iron occiirs constitutes the Mesabi range. This has been before regarded 

 as the base of the Keweenawan, into which it fades upwardly, but it has been 

 found that this great gabbro flow was outpoured at an earlier date, and it is 

 placed at or near the bottom of the Animikie. 



Considered as to origin, the ores of the Taconic found in groups 1 and 

 2 above are supposed to be due to chemical oceanic precipitation. Those 

 of group 4 are of igneous origin and are an integral part of the gabbro 

 The origin of those of group 3 is not definitely stated (pp. 144-145). 

 None of these Taconic ores are thus far mined in Minnesota. 



Batlet, W. S. Notes on the petrography and geologj' of the Akeley Lake 

 I'egion in northeastern Minnesota: Nineteenth Ann. Rept. Geol. and Nat. Hist. 

 Survey Minn., for 1890, 1892, pp. 193-210. 



This is chiefly a petrographic description of rocks from Akeley Lake. 

 The three important results reached, largely by the microscopic study, are 

 summarized as follows : 



(1) Most of the rocks designated as Pewabic quartzite in the neighborhood of 

 Akeley Lake are not quartzites, but thej' are granulitic j)hases of gabbro. The 

 remainder are crystallized aggregates of quartz. None of them are sedimentary 

 rocks, and consequently none can serve to determine the age of the ore associated 

 with them or of the gabbro in which they occur. 



(^) On the other hand, the granulitic gabbros may be traced into true granitic 

 gabbros and into quartzose phases of granulitic varieties. Hence, tlie granulitic 

 beds and their associated ores are of the same age as the gabbro, whose structural 

 relations to the younger and older formations must be appealed to in order to settle 

 the question of age. 



(3) Since so much of the "Pewabic quartzite" is not quartzite in any sense of 

 the word, and since different beds that have been given this name are not all certainly 



