892 THE PENOKEE IROXBEARIXG SERIES. 



ill character with these are found in the fragmental belt south of the yreen- 

 stone-conglomerate, in the southwest part of Sec. 19, and the northwest part 

 of Sec. 29, T. 47 Nl, R. 43 W., Michigan. So Hke are the exposures from 

 these different localities that one is inclined to explain their similarity by 

 supposing the area to have a structure which makes them contempo- 

 raneous in formation. It can as well be explained, however, b}' consider- 

 ing one of these belts as older than the other, the similarity being due t(i 

 the recurrence of like, or nearly like conditions at two different times. 

 In passing to the eastward, all the exposures in Sec. 13, T. 47 N., R. 44 W., 

 Michigan, 'and in Sees. 18 and 19, T. 47 N., R. 43 W., Michigan, are ferni- 

 ginous — ^most of them heavily. The larger part of the iron contained in the 

 rocks is in the form of hematite, although in some places magnetite is found. 

 In the northeast part of Sec. 19, T. 47 N., R. 43 W., Michigan, layers from 

 mere films to several feet thick are so largely composed of hematite as to 

 resemble somewhat an iron ore. This amount of iron oxide is so great as 

 to have encouraged explorers to follow these lieds to some de])th in the hope 

 of obtaining merchantable iron ore. In Sees. 17 and 20, and IG and 21, T 

 47 N., R. 43 W., Michigan, the exposures are much less heavily ferruginous 

 than farther to the westward. The amount of liematite and limonite 

 remains considerable, and this is particularly true in the south half of the 

 belt. The most of the iron is in the form of oxide as before, but witli tliis 

 iron oxide a considerable quantity of ferriferous carbonate is associated. Tlie 

 ferro-dolomite or siderite is seen in all stages of alteration to iron oxide, 

 the areas of the latter at times being beaiitiful pseudomorps. This car- 

 bonate is also accompanied by a good deal of finely crystalline or cherty 

 cjiiartz. In the cases of some exposures in Sees. 1 6 and 20, T. 47 N., R. 

 43 W., Michigan, the amount of nonfragmental material is fxdly as great as 

 the fragmental quartz and feldspar mingled with it. From the east side 

 of Sec. 15 to the east end of the area in Sec. 2S, T. 47 N., R. 42 W., Micli- 

 igan, the quantity of iron oxide contained in tlie belt is small. Ujion the 

 other hand, the amount of ferriferous carbonate and of clierty silica is far 

 greater than to the westward. The exposure in tlie eastern part of Sec. 

 15, T. 47 N., R. 43 W., Michigan, is in almost equal quantity fragmental 

 and nonfragmental material. In jdaces, in narrow l)aiids, cherty silica and 



