510 THE MARQUETTE IRON-BEARING DISTRICT. 



Magnetite grains are scattered evervwiiere throughout the section. The 

 rock of the second dike differs from that of the first one in being coarser- 

 grained. The chloritoid is developed in hirge plates whose pleochroism 

 is very marked in greenish-blue and yellowish-green tints. Biotite, musco- 

 vite, magnetite, and quartz are included in small quantity in most of the 

 plates, though some of them are entirely free from inclusions of all kinds. 

 Between the plates are little nests of calcite and large irregular areas of 

 plagioclase and its alteration products, chlorite, kaolin, quartz, biotite, and 

 needles of amphibole. The biotite is also present in large flakes of the 

 usual color, and the quartz in large, clear g-rains, the former mineral being 

 usually in the feldspar and at its contact with the chlorite, and the (piartz 

 occurring especially between chloritoid plates. 



The talcose-schists are rare. They are limited almost exclusively to 

 the ore horizons, where the processes that have resulted in the accumulation 

 of the ores have at the same time leached the iron salts from schistose 

 diabases and made them talcose-schists instead of chlorite-schists. By 

 further leaching magnesium is removed and the schists become kaolin- 

 schists. Some of the iron salts abstracted from the diabases may have 

 aided in the formation of the ore bodies, but they certainly did not con- 

 tribute the main bulk of the ore deposits. 



The talcose-schists, "soapstones," and "paint-rocks" are varieties of 

 the same rock. They are all talcose-schists, which differ from the chlorite- 

 schists in the fact that their magnesian component is talc rather than a 

 chlorite. The "soapstones" are the almost pure, light-colored phases of 

 this rock, while the "paint-rocks" are varieties that have been colored red 

 or brown by the infiltration of red or brown ocher. Slany of these rocks 

 are so much decomposed that little remains to tell their history. The 

 "soapstones" are composed largely of quartz, talc, probably a little seri- 

 cite, and calcite. Chlorite is also present in most specimens. In some it 

 occurs in but small quantity; in others it is more abundant; while in still 

 others it is present in such large quantities that these rocks must be regarded 

 as linking the purer talcose-schists with the typical chlorite-schists. In 

 other words, there is an unbroken gradation between the talcose-schists and 

 the clilorite-schists. Since the latter are altered diabase dikes, the former 



