42 THE MARQUETTE IROISr-BEARIXG DISTRICT. 



and Wliitney's declaration tliat the greater portion of the specular jasper 

 is eru])tive. 



Tlie author descriljes the entire series of tlie iron-bearing rocks as 

 occurring in great flexures, with a uniform trend east and west. 



The position of the beds of si^eciilar iron ore [is] * * * at tlie top of the 

 Huroniau series as developed in the Marquette region, and * * * tbey are inter- 

 stratified witli tiilcose and argillaceous schists. Sharing' the plications of the entire 

 series, these specular schists, as they may properly be called, are accordingly folded 

 into synclinal basins and anticlinal crests, of which the axes in the case of the former 

 lie below drainage, in the bottoms of the valleys, and in the case of the latter are 

 commonly obliterated through the erosion of elevated outcrops. * * * 



The bosses of specular iron, tlie iron knobs, * * * are the most striking 

 examples of exception to the general effects of denudation already noticed. They are 

 instances of the i)reservation of the anticlinal crest. * * * (P. 299.) 



The ores were observed to be associated with the schists in these folds, 

 and hence they must have been "under the saino conditions of deposit and 

 secondary modification" as these lattei*, which, it is believed, are meta- 

 morphosed sediments. 



The hard ores of the region are sliown to be genuine sediments. 

 We quote the author's own words (p|). 3()l-30"2): 



Beds of specular conglomerate are of frequent occurrence throughout the iron 

 region of northern Michigan, consisting of a paste of specular peroxyd of iron, 

 through which are disseminated fragments of jasper and rounded pebbles of specular 

 iron ore, which usually ditfer from the paste in texture, a difference very perceptible 

 among ores of any one class, even within narrow limits of distribution. These con- 

 glomerates not unfrequently resemble breccia in the angularity of the jasper frag- 

 ments which they contain; but the pebbles of specular peroxyd, although sometimes 

 obscure in a matrix of the same material, commonly serve to indicate the detrital 

 origin of these beds. That they are derived from local detritus is evident from the 

 fact that the jasper fragments are not rounded, while the particles of softer specular 

 iron ore are worn but slightly. They seem to be of littoral formation and to have 

 been derived from dismembered and crumbled deposits of successive lamin* of jasper 

 and iron ore, similar to those deposits distinguishable in the bosses of the region. The 

 specular conglomerate invariably exists under circumstances of true bedding, and is 

 traver.sed by parallel joints splitting the imbedded pebbles. It occurs interstratified 

 with talcose and argillaceous schists quite as regularly as the homogeneous ores. 

 * * * A specular conglomerate, uncontaminated with any considerable portion of 

 jasper, forms the bulk of the schists at present wrought by the Lake Superior mine. 



