CURRENT PRE- CA M BRIAN LITER A TURE 1 97 



The correlation of the Minnesota series with the Ottawa gneiss and 

 with the Finland series must be considered a pure conjecture. The 

 Minnesota succession is not agreed upon ; these widely separated 

 regions have not been connected by structural work, and of course in 

 the case of Finland never can be ; and lastly, fossil evidence is lacking. 

 Any correlation of the ancient crystalline rocks without the basis of 

 connecting structural work or fossil evidence, must be considered as 

 little more than a guess, having no foundation in inductive knowledge. 



The massive igneous rocks of the Laurentian, mostly granites, 

 which intrude the sedimentary rocks, are believed by Winchell to be 

 due to the aqueo-igneous fusion of the lower portion of the sedimen- 

 tary rocks, and the intrusion of the magma thus formed into the over- 

 lying sediments. The argument adduced in favor of this origin is 

 based almost entirely upon an occurrence cited at Kekequabic Lake of 

 a transition from igneous rocks to the clastic rocks there found. In 

 1891 and 1892 Grant 1 studied this area, and found no evidence of a 

 transition from the semicrystalline and crystalline schists into granite. 

 On the contrary, abundant evidence was found of the eruptive nature 

 of the granitic rocks in the surrounding sedimentaries. The same area 

 was closely studied by a party of the U. S. Geol. Survey during 1898, 

 and the same conclusion was reached. The principal support of Win- 

 chell's theory is thus taken away, and it stands as an unproved hypoth- 

 esis. 



Grant 2 describes and maps the geology of Kekequabic Lake in north- 

 eastern Minnesota. By far the larger proportion of the rocks repre- 

 sented are elastics, which are divided 'for convenience into four groups. 

 The first and most extensive group is the slate formation, consisting 

 largely of argillites, with smaller amounts of fine and coarse graywackes 

 and grits, the coarser phases becoming distinctly conglomeratic in 

 places. The second group consists of coarse conglomeratic rocks, which 

 are a part of the Ogishke conglomerate. The third group is made up 

 of certain fissile green schists, which are believed to be water deposited, 

 and probably originally formed from fine volcanic ash. The fourth 



'Twentieth Ann. Rept. Geol. and Nat. Hist. Surv. of Minn., 1893, pp. 69-82 ; and 

 Twenty-first Ann. Rept., ibid., pp. 50-54. 



2 The geology of Kekequabic Lake in northeastern Minnesota, with special refer- 

 ence to an augite soda granite, by U. S. Grant : A thesis accepted for the degree of 

 Ph.D in The Johns Hopkins University, 1893. Published in Twenty-first Ann. Rept. Geol. 

 and Nat. Hist. Surv. of Minn., for 1892, pp. 5-58, 1893. With geol. map and plates. 



