XXIV Ol'TLlNE OF THIS MONOGRAPH. 



bauds is stained red liy inclnded liematite. The iiou ores resulted from the couceutratioii of the iron 

 oxides through the ai^euey of dowuward-percolating waters. Tliese couceiitratiou-bodies usually occur 

 upon iuipervious basements in pitching troughs. The pitching troughs are formed by the Siarno slate, 

 the Ajibik quartzite, a mass or dike of greenstone, or by some combination of these. The ore deposits 

 are likely to be of large size where as a result of the folding the iron-bearing formation is much frac- 

 tured, thus permitting the ready action of percolating waters. The ore deposits occur at the bottom 

 of the Negaunee formation, within the Negannee formation, and at the junction plane between the 

 Negaunee formation and the overlying Ishpeming formation. From the position of the ore deposits 

 above the impervious formations it is concluded that their concentration occurred during or subsequent 

 to the folding which took place later than Upper Marquette time. 



Chapter IV treats of the Upper Marquette series. This series is composed of the following 

 formations, from the base upward: The Ishpeming formation, the Michigamme formation, the Clarks- 

 burg formation. As in the case of the Lower Marquette series, for each formation the distribution, 

 exposures, topography, foldiug, relations to adjacent formations, petrographical character, thickness, 

 and interesting localities are discussed. 



The Ishpeming formation includes two classes of rock, which are called the Goodrich quartzite 

 and the Bijiki schist. These rocks are sufBciently different to have different formation names, but 

 the Bijiki schist for the west eud of the district occupies a part of the horizon of the Goodrich 

 quartzite in the central part. The quartzite, from 600 to 1,550 feet thick, is confined to the central and 

 western parts of the district. The main area of the formation is folded into a synelinorium, which, as 

 a result of a western pitch, terminates to the east at Ishpeming. On account of the resistant character 

 of the formation, for much of the district it constitutes a ridge separating the less resistant Negaunee 

 formation below and Michigamme formation above. The Goodrich quartzite rests unconformably upon 

 the Negaunee formatiou. For the greater part of its area it grades up into the Michigamme or Clarks- 

 burg formations, but in the northwestern part of the district it passes into the Bijiki schist. The 

 least metamorphosed rocks are quartzites and quartzite-conglomerates, the grains of which show pres- 

 sure effects. The more metamorphosed rocks have been so mashed as to have become schist-conglom- 

 erates and micaceous quartz-schists. Where the formation rests upon the Archean the mica-schists and 

 mica-gneisses also occur. Between the various kinds there are all gradations. At the base of the 

 Goodrich <iuartzite is a basal conglomerate. For the major part of the district this conglomerate rests 

 upon the Negaunee formation. Its detritus is therefore derived mainly from that formation, and the 

 rock is an ore, chert, jasper, and quartz conglomerate. At a few places the Archean rocks are subjacent, 

 and their materials predominate in the conglomerate. The Bijiki schist, from to 520 feet tliick, is con- 

 fined to the western part of the district. The rock is a banded griiuerite-maguetite-sohist, which has 

 been derived by metasomatic and dynamic processes from an impure siderite. 



The Bijiki schist grades into the Goodrich quartzite below and into the Michigamme formation 

 above. 



The Michigamme formatiou occurs in a single large belt, stretching from the center to' the western 

 end of the district. It is folded into a great composite syncliue at the center of the Marquette syn- 

 elinorium. The rocks were originally ferruginous and nonferrnginous muds and grits. These have 

 been altered to slates, graywackes, mica-schists, and mica-gneisses. In this transformation the feld- 

 spars have decomposed to quartz and mica, the fragmental (luartz has been granulated, and the most 

 metamorphosed of the resultant rocks are foliated, completely crystalline schists. The formation 

 grades below into the Goodrich quartzite, Bijiki schist, or Clarksburg formatiou. Its thickness is very 

 considerable, probably 2,000 feet or more, but no accurate estimate can be given. 



The Clarksburg formation differs from the other formations of the Marquette series in that its pre- 

 dominant rocks are composed of volcanic materials. The formation embraces basic lava flows, tuffs, 



