

146 THE PENOKEE IRON B EASING SERIES. 



Thiclnii'ss. — 111 scverjil ])ltices the full surface width of tlie Quartz-slate 

 uieiiilier is fuutinuuusly exjxtsed, while in other places exposures of the rocks 

 north and south of it limit its possible width in such a manner that we 

 can tell \(^v\ closely the true thickness. Tliis surface width, while of 

 course primarily dependent u])oii the thickness of the layer itself, is also 

 dependent hu-yel}' upon the degree of its inclination to the north, which 

 varies from 4(1" as a minimum, to 75° as a maximum, although the 

 extremes are rarely reaciuMl, tlie usual figures lying between 55" and 65°. 

 The following arc the approximate thicknesses observed at various points, 

 l)eginning on tlie west: In the northern i)art of Sec. 24, T. 44. N., R. 4 W., 

 Wisconshi, 400 feet: at the passage of Bad river. Sec. 14, T. 44 N., R. 3 W., 

 Wisconsin, 41 feet ; at mount Wliittlese}', near the northwest corner of Sec. 1 6, 

 T. 44 N., R. 2 W., Wisconsin, 400 feet; at the })assage of the Potato river, Sec. 

 19, T. 45 N., K. 1 E., Wisc( >nsiii, 425 feet ; at the passage of the West branch of 

 the Montreal river, Sec. 27, '\\ 4(5 N., R. 2 K., Wisconsin, 467 feet. At the Aurora 

 mine, NE. \ Sec. 24, T. 47 N., R. 47 W., Michigan, the observed thickness is 

 300 feet, l)ut the eiitiiv thickness is not exposed, the greatest ])ossible thick- 

 ness between the granite oii tlie soutli and the Iron-bearing member on tlie 

 north being 545 feet. Similarh' on the west side of Sec. 13, T. 47 N., R. 

 46 W., Michigan, tlie greatest possible thickness is 564 feet. Farther east the 

 formation thickens somewhat rapidl}-, partii-ularly east of vSunday lake. In 

 the northern part of Sec. 10, T. 47 N., R. 45 W., Michigan, there is a contin- 

 uous exposure aljout ',(HH)teet wide, which, with the di]) of 55°, corre- 

 si)onds to a thickness of at least SOO feet. Tims it apj)ears that from the 

 western end of the Renokee range to the passage of the Potato river there 

 is an almost constant thickness of 400 feet: that ea.st of Potato river there 

 is a very gradual increase in thickness, wliicli, at the passage of the West 

 branch of the Montreal, is nearly 500 feet; and that this gradual increase 

 continues until the vicinity of Suiwlay lake is reached, when a mQva rapid 

 increase occurs, tlie maximum of 800 feet being reached about 2 miles east 

 of that lake. 



Gnwrdl pityofirdjihiidl ilKtrditcy mid stratifirapliy. — The rocks of this 

 formation have in common, witli the exceptioi of its uppermost horizon, a 

 strong slaty tendency and liglii colored weathering; the slaty structure 



