166 THE CRYSTAL PALLS IRON-BEARING DISTRICT. 



derivatives; and tliinly laminated chert)^ siderite-slate, ferruginous chert, 

 and ii-(in ores. Witli these we find only in two places rocks of a well- 

 developed conglomeratic nature. 



Some of the rocks have undergone great metamorphism, and we find 

 the graywackes and slates passing into chlorite-schists, mica-schists, and 

 mica-gneisses. The ore deposits of the district are associated with the least 

 altered sediraentaries. 



The graywackes and slates are found chiefly in the northern and 

 Avestern parts of the district, while the single conglomerate, the metamor- 

 phosed or micaceous graywackes and slates, the mica-schists, and the mica- 

 gneisses are confined to the southern portion. 



Near Crystal Falls on both banks of the river, between the wagon and 

 railroad bridges, there is exposed a conglomeratic phase of graywacke. 

 Several bands of these coarse conglomeratic graywackes are interlaminated 

 with bands of fine-grained graywacke and chert. A well-developed chert 

 reibungsbreccia is also associated with these. I do not consider this con- 

 glomei'atic graywacke as representing anything more than a purely local 

 and very slight unconformity. This is evidently the same occurrence of 

 conglomerate whicli has already been mentioned by Wadsworth.^ 



The well-developed conglomerate found in sec. 9, T. 42 N., R. 31 W., 

 along the Michigamme River, contains pebbles of both basic and acid 

 eruptive rocks in a chlorite-schist matrix. Toward the south the rock 

 grades up into chloritic graywackes and chlorite-schists, which possess the 

 ordinary characters of similar rocks in other portions of the area. The 

 graywackes and slates of the district in general differ from each other 

 chiefly in coarseness of grain. They are commonly interbedded in the 

 same exposures. The rocks vary in coarseness from medium-grained 

 graywacke to aphanitic slates, and in color from gray to green and black, 

 the aphanitic slates being usually the darkest. These fine-grained rocks 

 always show well-developed slat}'- cleavage. Throughout the area the 

 rocks are very thoroughly consolidated, and in places where they have 

 been most altered they are completely crystalline schists. 



The crystalline rocks which are believed to have developed from the 

 elastics are found in the southern portion of the district, beginning in 

 sec. 16, T. 42 N., R. 31 W., and are well exposed in the river section at Nor- 



' Sketch of the geology of the iron, gold, and copper districts of Michigan, by M. E. Wads- 

 worth: Ann. Kept. State Board of Geol. Survey for 1891-92, 1893, p. 128. 



