198 THE PENOKEE IRON-BEARING SERIES. 



hematite; VI, 27 per cent of magnetite and 48 43 per cent of hematite. For 

 VII the figures are 54-12 and 3-91; for VIII, 3973 and 1301 ; for IX, 16-27 

 and 28-83. 



Distrihufion of the three types of rock. — In all that portion of the Iron- 

 bearing member which lies to the west of the passage through the Penokee 

 range of Tylers fork, in Sec. 33, T. 44 N., R. 1 W., Wisconsin, the rocks of 

 the third type or actinolitic and magnetitic schists prevail ; in fact, except 

 that the rock of certain exposures, much more highly quartzose than usual, 

 ap))roaches the cherts of the second type, it may be said that these rocks 

 are the only ones met with. At the gorge of Tylers fork, however, the 

 actinolite has almost, though not quite, sunk out of sight, while the siliceous 

 constituent is altogether the most prominent one. At the same time hema- 

 tite and brown iron oxides begin to prevail over the magnetite. 



To the east of Tylers fork the first and second types greatly pre- 

 dominate, though phases carrying minute quantities of actinolite continue 

 to occur as far east as the Potato river. Nevertheless, these are very rare, 

 and nowhere in this portion of the range has any highly actinolitic rock yet 

 been met with. Just where these actinolitic rocks cease it is difiicult to tell, 

 but they can not continue far to the east of Tylers fork, not far from 

 which stream the cherty and carbonated rocks of the first and second types 

 have increased to such an extent as to occupy the whole of the iron belt, 

 the frequent occurrence of bodies of hematite ore at the base of the member 

 beginning at the same time with this change. For some 30 miles no^^' to 

 the east, or as far as near the east side of T. 47 N., R. if-) W., Michigan, 

 the cherts and carbonates, with iron ore bodies at or nciir tlie liase of the 

 formation, continue nearly to the exclusion of the actinolitic rocks. In this 

 distance is included with few exceptions all of the working mines of the 

 Gogel>ic districts. The somewhat magnetitic and actinolitic rocks just west 

 of Tylers fork include one mine, and the somewhat actinolitic and magnetitic 

 rocks in T. 47 N., R. 45 W., Michigan, include several. A rude subordinate 

 .stratigraphic aiTangement in the iron belt appears to hold for this distance; 

 i. e., the purer carbonates are characteristic of the upper liorizuns, the fer- 

 ruginous slates of the middle horizons, while the ferruginous cherts and ore 

 bodies lie within the lower horizons. It is not inciint to indicate by this 



