96 THE VERMILION IRON-BEARING DISTRICT. 



the intervals between such gneissoid areas the semiciystalline schists prevent 

 the structure of a simple synclinal fold. Petrographically the semicrys- 

 talline schists (Keewatin) are sericitic schists inclosing beds of hematite, 

 argillite, including the Ogishke-Muncie conglomerate, porphyrellite and 

 chloritic schists, porodites, agglomerates and tuffs, and graywackes. 



Wherever the crystalline and semicrystalline schists are seen in juxtaposition 

 their stratification is strictly conformable. Wherever the crystalline schists are 

 wanting the semicrystalline schists are found in conformity with the gneisses. 

 Moreover, whether the semicrystalline schists occur in juxtaposition with the crys- 

 talline schists or the gneisses, there exist frequently those transitions bj^ alternation 

 which characterize the passage from the crystalline schists to the gneisses. This 

 mode of transition, however, is much the most characteristic of the passage from 

 the semicrystallines to the crystallines [p. 383]. 



Statement is also made of the petrographic gradation between the 

 semicrystalline and crystalline schists. 



The uncrystalline schists (Animikie) are chiefly thin-bedded black 

 argiUites grading into graywackes and even into conglomerates, with flint 

 and. jasper schist and beds of magnetite. These rocks overlie the semi- 

 crystalline Keewatin schists with strong unconformity. 



The enumeration made embraces all rocks up to the Keweenawan. 

 So far as these groups are concerned the order, in descending succession, is 

 as follows: 



5. The uncrystalline schists (Animikie, Huronian). 



4. The semicrystalline schists (Keewatin). 



3. The crystalline schists (Vermilion). 



2. The gneissoid rocks 1 ,_ ^. , 



-, rp, -. -J 1 • (Laurentian). 



1. ihe granicoid rocks j 



WiNCHELL, N. H. and H. V. The Taconic iron ores of Minnesota and of 

 western New England: Am. Geologist, Vol. VI, 1890, pp. 263-274. 



In 1890 N. H. and H. V. Winchell state that the iron ores of Minne- 

 sota are, at five different geologic horizons, in descending order, as follows: 

 (1) The hematites and limonites of the Mesabi range, the equivalents of 

 the hematites of the Penokee-Gogebic range in Wisconsin; (2) the gabbro 

 titaniferous magnetites near the bottom of the rocks of the Mesabi range; 

 (3) olivinitic magnetites, just below the gabbro in the basal portion of the 

 Mesabi rocks; (4) the hematites and magnetites of the Vermilion range 



