THE QUAETZ-SLATE MEMBER. I45 



Topographkal fraiurcs. — At tlie western end of the Penokee range the 

 layers of tlie <^)iuirtz-shite inenibcr form the base of the southern sh)|)e of 

 the ranyc. From liere eastward, liowever, the shite rises higher and 

 higher on this sh)pe, forming fretiuent bokl and even precijjitous soutli- 

 facing exposures. At Bad river tlie shite reaches nearly, and at mount 

 Whittlesey, See. 1G,T. 44 N., R. 2 W., Wiseonsin, quite, to the top of the ridge. 

 Still farther east it forms iiKtre and more of the l)ulk of the range; while 

 to the east of Tylers fork the whole width of the outcrop lies on the 

 northern slo})e of the range, the summit here lying within the Southern 

 Comjdex. The same is very noticeably true in the (liogeljic countrN', east 

 of the state Ijoundary, the slate as far as the vicinit>' of the West branch <>f 

 Black river forming the northern slope ot a bold ridge whose summit lies 

 within the granite. To the east of the West branch of Black river another 

 change in this respect takes place, the ridge itself lying within the jaspery 

 iron l)elt noi-th of the (piartz-slate, which now lies in the lower ground to 

 the southward; while beyond Sunday lake and as far east as the East 

 l)ranch of Black river, the (j[uartz-slate again appears in l)old exjxisures, 

 and now forms the principal ridge, with low ground nortli and south of it. 

 This varying position of the crest of the ridge with regard to the different 

 I'ock belts is plainly a result of the varying relations between the several 

 belts as to power of resisting erosion. At the west the Quartz-.slate 

 member contains an unusually large amount of soft chloritic slates and 

 relatively little of highly quartzose jiortions, whilst at the same time the 

 iron belt inuuediately nortii of it is exceedinglv quartzose and I'esist- 

 ant. Farther east the quartz-slate l)ecomes more and more liighK' (piartz- 

 ose, and hence resistant, and now goes along with the iron Ix'U itself to 

 make up tlic^ bulk of the ridge. After Tyler's fork is passed, liowever, the 

 iron belt begins to lUKhn'go a change \\liereb>' its resisting powi'r becomes 

 less and less, and, as the Montreal river is neared, the granite to the south 

 becomes the most resistant rock, and the crest of the ridge is on it. In the 

 same way a. connection Itetween the different degrees of resisting- ])ower of 

 tlie vai'ious I'ocks, and the position of the crest of the range, may be shown 

 to hold tor ihat portion of the distance east of the West branch of Black 

 river. 



MON XIX 10 



