THE EASTERN AKEA. 363 



greater <tr less (luaiititv of mechanical sediments. This minp-lino- of fra<>- 

 mental and nonfragmental sediments has occurred so extensively in the 

 eastern area that a new color is used upon Pis. ii and xiii to desionate 

 this additional phase of rock. This color is intermediate between the 

 yellc^w of the Quartz-slate member and the brown of the Iron-bearing 

 member. It is thus chosen because the ledgres so marked contain a larsre 

 amount of both- fraginental and nonfragmental material, and are therefore 

 intermediate between the two members. This new characteristic of the 

 rocks of the series is noted as far west as in the west part of Sec. 17, T. 

 47 N., R. 44 W. Here are cherts and jaspers which contain a varying and 

 even a large amount of fragmental (juartz and feldspar (PI. xxxv, Fig. 1). 

 Apparently interstratified with these locks are clay -slates which are largely 

 mechanical sediments, although it is difficult or impossible to determine 

 exactly what proportion of the very fine material in these slates is frag- 

 mental and what nonfragmental. 



In Sees. 19, 20, 21, 22, and 23, T. 47 N., R. 43 W., Michigan, the iron- 

 Ijearing rocks have been located in many places by explorations, lint the 

 numerous test pits there sunk have as often struck the soft chloritic slate 

 as the iron-bearing rocks proper. The cross-cuts from these test pits 

 clearly show that in the distance north and south through \vliich the iroa- 

 bearing rocks occur there are also several or many intermediate layers of 

 clay-slates or other partially fragmental rocks, and in some cases there is 

 interstratified with the iron-bearing rocks a vitreous quartzite. The succes- 

 sion of i-ocks in Sec. 21 is as follows: At the south are well developed 

 exposures which belong to the feldspathic quartz-slates, the exposures con- 

 taining both the characteristic variegated slates, and }d1o^'e these next to 

 the iron formation a vitreous quartzite. To the north follow a series of Inter- 

 laminated cherty ore formation rocks and chloritic slates of some thickness. 

 Farther/to the north in a test pit is shown vitreous (piartzite, the particles 

 of which m-e chiefly large grains of (piartz wliich have had a second 

 growth. Still farther to the north is again found lean chert v ores, and 

 again north of these, after jmssing an interval of some distance which is 

 unexplored, is found a wide belt of ferruginous fragmental slates. Where 

 the slates belong in the succession will be discussed later; but disreirardinir 



