380 THE PENOKEE IRON-BEARING SERIES. 



mingled iiourlastic ;iu<l clastic .sediment. If this is the origin of this jasper- 

 cong-lomerate it is a, strong indication that the greenstone-conglomerates, 

 which dift'ci' from it onU' in the absence of jasper fragments, are of a like 

 character. It follows from the above that the class of conglomerates which 

 contain a preponderating amount of nonfragmental material are closely 

 allied to the rocks of the Iron-bearing member of the Penokee series. The 

 contained fragments of l)asic eruptives is the chief point in which they are 

 unlike this ii'on-bearing belt. This phase of the greenstone-conglomerates 

 is still more nearh' like in essential clKiracter the ferruo-iuous and frasf- 

 mental I'ocks iiorth and sonth of the greenstone-conglomerates, the chief 

 difference between the two classes of rocks being that the complex basic 

 eruptive fragments take the place of the simple quartz, feldspar, and clayey 

 fragments of these lielts. It has been noted that closely mingled with the 

 greenstone-schists and greenstone-ct^nglomerates are a i'ew rocks Avhich are 

 essentially like the ferruginous and fragmental rocks to the north and east. 

 It would appear that in these eases for a short time mingled fragmental 

 and nonfragmental sedimentation has occurre<l without having received 

 basic ej-uptive debris. In these interlaminated rare varieties of rock we 

 have still another link lietween the greenstone-conglomerates and the 

 ordinary ferruo'inous and fraomental helt to the north and east. 



From the foregoing it would appear that in the greenstone-conglomerate 

 area and vicinity we have gradations from a rock which is a ])urely basic 

 erupti\'e amygdaloidal flow to those which are simply mingled clastic and 

 uonclastic sediments. Intervening between these widely separated phases 

 are the bn^'ciateil rocks, A\'liich appear to liave had a lava base and contain 

 fragments of essentiidlv the same material ; rocks which appear to be tuffs 

 alone; rocks in which tnff has fallen upon water aii<l has become mingled 

 with water-formed detritus and, varying from this b}' a gradual lessening 

 of the tuff, rocks which are simpl}^ mingleil fragmental and nonfragmental 

 water-deposited sediments. 



Whether all of the above conclusions as to the origin of the different 

 phases of this rock are true or not, it is certain that this area has been the 

 center of great volcanic activit\'. This is evidenced bv the great masses 

 of greenstone in Sees. -If, and "27, T. 47 N., II. 44 W., Michigan, by the 



