34 Van Hise — Iron Ores of the Penokee- Gogebic Series. 



bodies. The carbonate lias proved to be far more abundant 

 than was supposed when the paper alluded to was written, and 

 is found at all horizons, but most plentifully in the upper ones. 

 The regularly bedded ferruginous slates are prevalent in the 

 middle, and the ore bodies and ferruginous cherts at the lower 

 horizons. In this paper I have not space to add anything fur- 

 ther to what Professor Irving has said as to the j>articular 

 processes by which the different phases of rock, aside from the 

 ores, have been produced. 



Position of the ore in the iron-bearing member. — The iron- 

 ores are all located, as far as known at present, in that part of 

 the iron-bearing formation between Sec. 33, T. 45 N., R. 1 W., 

 Wis., and the east line of T. 47 K, R. 45 W., Mich., a dis- 

 tance of about 30 miles. The greater number of the larger 

 deposits are found in the central half of this area. Also most 

 of the known deposits lie at the base, or very near the base of 

 the iron-bearing member ; that is, they rest upon or close to the 

 coarse-grained fragmental quartzite which constitutes the up- 

 permost horizon of the quartz-slates. The number of impor- 

 tant mines is about 23, and of these all have deposits upon the 

 fragmental quartzite except five, and three of these, situated 

 east of Sunday Lake, at the eastern extremity of the belt of 

 mines, have exceptional characteristics which exclude them from 

 the present discussion. It is true that three other mines have 

 also deposits which are north of the fragmental quartzite ; but 

 in one case, that of the Colby Mine (fig. 4), the two ore- bodies 

 have been shown by developments to have such connections as 

 to show that they are essentially a single deposit. It is not 

 meant to imply that the numerous deposits resting upon the 

 foot-wall quartzite have clean ore always in contact with it. 

 Quite often there is a layer of what the miners denominate 

 " paint rock," or a layer of sand rock between the quartzite 

 and the ore. This latter material is sometimes as much as 20 

 feet in thickness, although it is usually not more than a few 

 inches, or at most a few feet. Sometimes also there is, be- 

 tween the ore and the quartzite, a mass of greater or less thick- 

 ness of the ferruginous chert or mixed ore of the miners; 

 rarely a thin layer of nearly pure white chert is found between 

 the ore and quartzite. Notwithstanding these exceptions, the 

 south side of the ore never penetrates the quartzite and in a 

 general way follows it, so that it may be spoken of as resting 

 upon it. This quartzite, although subject to local variations, 

 has an average dip to the north of 60° to 70°, and thus fur- 

 nishes an approximately regular wall, north of .which the ore 

 lies, and is consequently called the foot-wall by the miners. 

 The few deposits north of the foot-wall quartzite are described 

 by Mr. J. Parke Channing as also having regular south walls 



