PLATE LXXV. 



VIRGINIA PLATE OF THE MESABI IRON RANGE, 1899. N. H. WINCHELL. 



Within the area of this plate are some of the principal mining centres of the 

 state, viz., at Virginia, Eveleth and Biwabik. The rocks of the Animikie here swing 

 out from their normal strike, toward the south about seven miles, forming a loop 

 about a spur of the Archean. They dip in all directions from this Archean spur, 

 and also are thrust northward onto the Archean area, at the western base of the 

 spur, the taconyte horizon running beyond the limit of the quartzyte. According 

 to Mr. Spurr there are several instances of irregularity in the normal superposi- 

 tion and geographic location of the parts of the Animikie. These are not all repre- 

 sented on this plate (see Bulletin x). These abnormal conditions abnormal for a 

 wholly sedimentary rock are entirely consistent with the normal action of volcanoes 

 or other igneous ejections such as are necessary if the taconitic greensand was due 

 to an original volcanic source. 



The Archean granite rises in isolated knobs at three spots in the Archean spur 

 which, as a whole, is composed of characteristic Keewatin. The conglomeratic 

 composition seen at the railroad cuts in sees. 15 and 22, T. 58-17, within a mile east 

 of Mariska, indicates that the base of the Upper Keewatin is here seen. Between the 

 Keewatin and the granite at the northeast corner of the plate a narrow belt of 

 crystalline schists runs three or four miles. 



The black slates are well known in this area. Their lowest strata are some- 

 what calcareous, and in places they become flinty. When they are flinty, and are 

 near the taconyte, the iron frequently takes the form of siderite. 



The Cretaceous has been found in the area of this plate and has furnished fossils 

 of Ostrea, Inoceramus, Modiola, Pinna, Yoldia(?), Trigonarca Actgeon, Trochus and 

 Fasciolaria. The "gravel ore" found at the Lone Jack mine is probably a coarser 

 portion of the Cretaceous near its base. N. H. w. 



