440 • THE PEXOKEE IKON-BEARING SERIES. 



closely like one another, and so little is known of the relations of tlie rocks of 

 the Southern Complex to one another, that its direction can not, bevond tliese 

 limits, be made out. If the greenstone upon Bad rhev is taken to be an 

 mterbedded How, it appears that the fault line [jasses jjetween this and the 

 black slates east of this place on the railroad; but if it is an eruptive dike 

 cutting across the formation, as is probable, it gives no indication of the 

 location of the fault line. 



Fault at Potato river. — At Potato river, near the east side of Sec. lit, T. 

 45 N., R. 1 E., Wisconsin, there is again strong evidence that a fault exists, 

 although here the throw is not so great as at Bad river. The relations of 

 the exposures are exhibited b}' Fig. 6. Upon the east side of the river is a 

 larg-e exposure of green schist belonging to the Basement Complex. The 

 Quartz-slate is in contact with the schist and extends northward in contin- 

 uous exposure, with only a very slight break throughout its whole thick- 

 ness. North of and immediately adjacent to the vitreous quartzite, con- 

 stituting tlie uppermost member of this slate, are exposures of the Iron- 

 bearing member. The strike of the slate east of the river is west 20° south. 

 On the west side of the river large exposures of the underlying green schist 

 are noted. North of these follow smaller exposures of quartz-slate, and still 

 farther north the vitreous quartzite, and above this the rocks of the iron- 

 bearing belt; so that ea.st and west of the river we have the exact location 

 of the junction between the quartzite and iron-bearing belt, whiU- east of 

 the river is known the exact contact of the (piartz-slates and the under- 

 lying schists. Now, it is manifest that the large exposures of g-reen si'Iiists 

 west of the river lie directly athwart the course of the quartz-slates. The 

 same is true of the quartz-slate and quartzite on the west side of the river 

 as compared with the rock^s of the iron belt on the east side. Here, again 

 it may be suggested that a sharp bowing Avill explain the structure, and 

 hence a fault is not necessary to explain the facts; but between the slates 

 and the nearest schistose rock there are but 200 feet of space, in which a 

 much greater thickness of slates must pass. Further, there is absoluteh' no 

 indication by a change of direction of the strike of the slates that auN such 

 1)o\'^no-has here occurred. If the whole of the discordance here is taken to be 

 due to the fanlt, the liorizontal throw amounts to 2l~i() feet, as determined by 



