DENUDATION OF THE MARQUETTE DISTRICT. 573 



merely blufty. The hig-liest point in tlie district, the so-called Summit 

 Mountain, is 1,800 feet above the sea. The level of Lake 8ui)erior is GOO 

 feet; so that the maximum relief of the district is about 1,200 feet. Begin- 

 ning at the lake, there is a rapid rise to Negaunee, perhaps 10 miles, the 

 avei'age level there being about 1,400 feet. This eastern slope is a part 

 of the great Lake Superior basin. From Negaunee to the west end of 

 the district, that is, for much the larger part of the area, the variations 

 in elevations are scarcely more than 400 feet. The present differences of 

 elevation, with the exception of the eastward slope to Lake Superior, are 

 mainly due to differential erosion. The hard rocks, whether jusjiilites, grii- 

 nerite-magnetite-schists, quartzites, conglomerates, or greenstones, occupy 

 the higher elevations, and the soft rocks, the slates, shales, and most of the 

 iron-formation rocks, occupy the valleys and swamps. Since the forma- 

 tions south of ^Marquette were raised high by the eastern anticline, and 

 the whole district has been truncated to an approximate plain, it follows 

 that in the eastern end of the district all but the lowest formations have 

 been removed. Thus south of Marquette we find only the two lowest 

 formations of the Marquette series. Li the great syncline between the 

 Marquette anticline and the Michigamme anticline newer and newer forma- 

 tions come in, until the highest member of the Upper Marquette series 

 appears. The Michigamme anticline apparently was not so high as the 

 Marquette anticline, and therefore the higher members of the series are 

 exposed. However, we can not be sure that several of the remaining 

 Marquette formations would not have been removed were the plain of 

 denudation 600 feet lower — that is, at the elevation of Marquette. 



METAMORPHISM. 



The various formations of the Marquette series differ from one another 

 in hardness and coarseness of grain. It is probable that metasomatic and 

 cementing processes had taken place to some extent before the folding- 

 subsequent to Upper Marquette time, and thus they probably differed in 

 strength. When this period of folding occurred tlie varying texture and 

 strength were important factors in the resultant deformations, so that the 

 readjustments necessary in the folding took place in large measure between 



