374 THE PENOKEE IRON-BEARING SERIES. 



SECTION III.— THE GREENSTONE-CONGLOMERATES. 



Distrihiit'inn. — Tlie gTeenstone-cougloiiierates are restricted to tlie area 

 re])resented in PI. xiii, occurring nowhere except in T. 47 N., R 43 W., 

 and R. 44 W., Michigan. It will be seen that their westernmost appearance 

 is in the extreme northeast i)art of Sec. 16, T. 47 N., R. 44 W., Michigan. 

 In the northwest i)nrt of Sec. 14, T. 47 N., R. 44 W., Michigan, are areas 

 which are mapped as detached from the main mass of conglomerate because 

 they are not known to be connected with it. From the exposui-e in the south 

 part of Sec. 15, T. 47 N., R. 44 W., a belt of the conglomerate continues 

 eastward, rapidly widening, and in Sees. 24 and 25, T. 47 N., R. 43 W., 

 reaches its maxium width. If miles. Continuing eastwai-d, the belt quite 

 rapidl)^ narrows, and its last appearance is in the northwest pai-t of Sec. 23, 

 T. 47 N., R. 43 W., Michigan. The exposures of eruptive rocks in Sees. 

 13 and 14, in the west part of Sec. 23 and in the northeast part of Sec. 24, 

 T. 47 N., R. 44 W., Michigan, have all the characteristics of surface flows; 

 that is, they contain minerals .of two generations, are often amygdaloidal, 

 and have a groundmass which Is frequently partly amorphous and is always 

 finely crystalline. These exjjosures are believed to be more closely allied 

 to the o-reenstone-como-lomerates than to the diabases of the Penokee series. 



General characteristics. — The term "greenstone-conglomerate" is applied 

 to the rock of this area because it is a fragmental one, in which nearly all 

 the fragments are from basic eruptives, as is also the major jjortion of the 

 matrix in which these fragments are set. The term "agglomerate" would 

 convey a false impression. The rocks covered l>y the term greenstone- 

 conglomerate include agglomerates and water-deposited elastics, the detritus 

 of which is chiell\- from greenstones,' as well as gradations between these two 

 extremes. Macrosco])ically, the rocks vary from an aplianitic slate'" to a 

 coarse conglomerate. At times the tine grained clay-slates and the con- 

 glomerates are intimately mingled, but in general the slate exposures are 



'The word {irnciistime is used here in its old sense, ti> eover nil the liiisie eriiijtives of the distriet. 



='A rock reni:irl<:ilily siniihir to m;iny ot these coll{;h)ln<^r:lt('s is des(ril)ed liy (Jiimbel iiuder the 

 terra .Sih.ilsU'in. ((irniidziiue der (ieoloj;ie, pp. liK!, 197.) 'riu' nuitrires :iiid lim i t'lajiments of some of 

 the rucks in i|iieMtiiiii presiiil a schistose structure very similar to that li;;ured by him. The minerals 

 now present are identical with those contained in his schalstein, and his description could he applied 

 almost exactly to thcni. 



