GEOLOGICAL EXPLOEATIONS AND LITERATURE— 1873. 53 



auTliciiilivUite-sc'liists arc exposed at tlie Clianipi)ii i'urnaoe, where tliey 

 lie above the terruginous schist. Formation XVIII is not seen at Spurr 

 Mountain, liut it is found at the west end of Lake Michigamme, where it 

 ap])ears to he between the anthophylhte-schist (XVII) and the mica-schists 

 (XIX) exposed on the south shore and on the ishmds of the lake. The 

 bed is a gray quartzite, the supposed third quartzite of the region, to which 

 reference has ah-eady been made. The mica-schists are the youngest mem- 

 bers of the iron-bearing series, and are very abundantly developed. 



With respect to the position of the strata below V the author is not so 

 confident. He thinks that the iron ores and the associated rocks of the 

 Magnetic, Cannon, and Chippewa locations in the vicinity of Republic 

 belong here. These rocks are different from any of those described as 

 occurring in Formations XV-XIX. From their proximity to the Laurentian 

 they are supposed to be the oldest members of the Huronian. They are 

 beds of siliceous ferruginous schists, alternating with chlorite-schists and 

 diorite. 



The geological structure in the mines of the western portion of the 

 district is simple. It becomes more complicated in those in the vicinity of 

 Ishpeming and Negaunee. Beyond these towns the iron-bearing horizons 

 are lost. At the Lake Superior mines the ores are in a series of trouglis 

 with east-and-west axes. Above and below these are beds of chloritic 

 schists. On the east side of the mine the relations of the rocks are so 

 complicated that the author does mit attempt to explain them. 



The remarkable features are the great masses of liglit grayish-greeo chloritic 

 schist, having a vertical east-aud-west cleavage, no discernible bedding planes, and 

 holding small lenticular masses of specular ore, which couform iu their strike and dip 

 ■with this cleavage, and which seem to have no structural counection with the main 

 deijosits. They appear like dikes of ore squeezed out of the parent mass, which we 

 may suppose to have been iu a comparatively plastic state when the folding took 

 place; or they may have been small beds, contained originally iu the chloritic .schist, 

 and brought to their present form and c(mditiou by the .same causes, which produce[d], 

 the cleavage in the schist. (Pp. 130-lJ^O.) 



In the hanging wall of this mine Brooks found, instead of the usual 

 quartzite, a magnesian schist, similar to the schist associated with the ore.. 



