48 THE GEOLOGY OP MINNESOTA. 



[Extent of the Animikie. 



of the Keewatin, this being its position also in Ontario. Such a break in stratigraphy 

 implies a long epoch during which the folding of the Archean was produced. There 

 is no geological horizon between the Upper Cambrian and the Archean which seems 

 commensurate with these features except that which is usually put at the base of 

 the Lower Cambrian. 



Extent of the Animikie. Entering the state from the northeast at Pigeon point, 

 this formation runs westwardly along the international boundary to the vicinity of 

 Gunflint lake where it strikes into the state, to the vicinity of Chub (Akeley) lake 

 where it disappears. The manner of disappearance is interesting and suggestive. It 

 seems to separate into two parts for a short distance, one part leading into and 

 under the gabbro which penetrates it in the form of dikes and sills finally over- 

 whelming it, and the other running a few miles in an interrupted manner in a spur- 

 like prolongation further north. This spur-like northern prolongation is last seen (No. 

 1896) near the working of the Gunflint Lake Iron company's exploration, S. W. sec. 

 21, T. 65-4 W., at half a mile north from the gabbro mass, separated fi-om the gabbro 

 mass by an intervening belt of Keewatin greenstone belonging to the great greenstone 

 area of the region. It is known also to run eastward and to be the cause of several 

 iron locations. The southern edge of the exposure, in S. W. J sec. 21, shows a high 

 dip north, and, indeed, it is vertical in many places along the southern borders of 

 the mass. Then it bends, at lower levels, so as to be flat, and at favorable points of 

 view it can be seen to change from a vertical or northward dip to a southward 

 dip, there being a continuous swing between a southerly dip of 10 to 20 (extreme) 

 through horizontality to vertically. The flexure is abrupt and on the southern side 

 of the hill, the horizontal and southward dip being on the northern slopes. The 

 appearance, where the mass stands vertical, is very much like some black jaspery 

 outcrops in the Keewatin. The manner of superposition or contact on the green- 

 stone at this point cannot be seen. While this northern spur has been considered a 

 part of the Animikie, there are certain anomalous facts of position, structure and 

 petrography which, not having been seen elsewhere in connection with undoubted 

 Animikie, lead to the hypothesis that this part of the northern spur is a ferruginous 

 belt belonging to the Keewatin, and that the real strike of the Animikie is along the 

 southern spur mentioned, lost in the gabbro. 



A series of similar ferruginous outcrops occurring south westward further, begin- 

 ning with and including the "mine" of the Gunflint Lake Iron company at the centre 

 of sec. 28, T. 65-4 W., and extending along the stream westward from Akeley (Chub) 

 lake to Gabimichigama lake, Fraser lake, Thomas lake and Birch lake, as far as to 

 the appearance of undoubted Animikie in sees. 27 and 82, T. 60-13 W., fall into this 

 uncertain category, with probability of Keewatin age for all of them. These ores 



