156 THE MARQUETTE IRON-BE ARINC DISTRICT. 



The sfliistosity of tliese g-reenstoiies, which is seen both in the ledge 

 ;ui(i to a limited degree in thin section, where the chlorite s^jicules are found 

 to lie with their long axes in a uniform direction, is explained best as a 

 result of movement, as Williams has already observed. This geologist 

 declares that the study of these pale-green aphanitic greenstones seems to 

 indicate that they were not originally to any great extent tuff deposits, but 

 that they were massive flows of diabase, which have since suffered profound 

 chemical and stnu-tui-:il changes, in consequence of having been subjected to 

 intense (Unamic action. Perhaps the greater portions of tliese dense green- 

 stones were originally la\a flows, as suggested by Williams. A large portion 

 of them, however, were tuft" deposits. The signilicant fact in connection 

 with them is that they were all surface materials. 



Many of the dense schists have been weathered until the\' now consist 

 largely of calcite and epidote, so that no evidence of their original character 

 remains. 



The banded varieties. — Thc bauded sclilsts, best cxposcd in the northern 

 portion of the Mona schist area, are composed of alternate layers of 

 darker and lighter shades of green, giving- them a striped appearance. 

 Their texture is much coarser than that of the aphanitic greenstones 

 described above, and their structure is characteristically schistose. They 

 all contain an abundance of secondary amphibole* and consequently thev 

 are all more or less tibrous. Where their til)rosity is pronounced and tlieir 

 schistosity marked they form very fissile schists. Where the schistositv is 

 less marked the rocks may still be tibrous, but the fibers are grouped around 

 centers scattered through the specimen, and the rock has the aspect of a 

 uralitized diabase or gal)l)ro. 



On account of their l)an(led character these schists have been regarded 

 as sedimentary Ijy nearly all geologists who have studied them. "The 

 alternation in the color and composition of the lavers is so frequent and so 

 constant, and their parallelism to the east and west strike of all the rocks 

 of this neighborliood is so exact," writes Williams, "that no hypothesis of 

 their originally massive character will satisfactorilv account for the observed 

 facts. On the other hand, the chemical and the microscopical characters of 

 these schists agree closeh' with those of associated massive greenstones 



