56 THE MAllQUETTE IllOX-BEArtING DISTIJICT. 



aiul thiclciiess of rocks, aiiywlime iu tlie world, there is a larger percentage of irou 

 oxide than in the Maniuette series. In the order of relative abundance, so far as made 

 out, the ores are the Jimj, the red specular hematites, soft or brown hematites, and 

 magnetites. These all exist in workable beds, and all as disseminated minerals in 

 rocks usually siliceous. * * * So far there seems to be the greatest concentra- 

 tion of magnetic ores iu the Michigamme district of the Marquette region. From this 

 the relative proportion of magnetite seems to decrease as we go east, north, west, 

 and south. 



Next younger than the Huronian are the copper-bearing rocks of Keweenaw 

 peninsula, * * * the age of which has led to iiiuch controversy. * * * The 

 relations of the copper-bea ing rocks to the Huroniau are not fully made out. In 

 tracing the dividing line from Bad River in Wisconsin to Lake Gogebic, Michigan, 

 last fall * * * we found them nearly, if not precisely conformable, but widely 

 different iu lithological character * * *. 



The next series of rocks iu ascending order are the horizontally liedded Lower 

 Silurian sandstones, which skirt the south shore of Lake Superior nearly its whole 

 length, called by Foster, Whitney, and Dr. Eominger, Potsdam, and assigned by the 

 Canadian geologists, under the name St. Clary's, to a later period. * * * 



We will now return to the Huronian or highly magnetic series, taking up its 

 structure iu some detail. xVbout nineteen lithologically distinct beds or strata make 

 up the series; of these, six and probably seven are so magnetic as to cause con- 

 siderable variations iu the needle. These beds vary from 40 to several hundred 

 feet in thickness, and strike and dip in all directions and at all angles. The 

 prevailing strike, however, is easterly and westerly, and the dip at high angler 

 often vertical. * * * (Pp. 215-21S.) 



The sequence of the strata iu the ^Marquette seines is outhued as follows: 



I, II, III, IV are composed of beds of siliceous ferruginous schist, alternating 

 with chloritic schists and diorites, the relations of which have not been fully made 

 out; V is a quartzite, sometimes containing marble and beds of argillite and novacu- 

 lite; VI, VIII, and X are vsiliceous ferruginous schists; VII, IX, and XI are dioritic 

 rocks, varying much iu character; XIII is the bed which contains all the rich spec- 

 ular and magnetic ore, associated with mixed ore and magnesian schist; XIV is a 

 quartzite, often conglomeratic; XV is argillite or clay-slate; XVI is uncertain; it 

 contains some soft hematite; XVII is anthophyllitic schist, containing iron and 

 manganese; XVIII is doubtful; XIX is mica-schist, containing staurolite, andalusite 

 and garnets. * # * 



These beds appear to be metamorphosed sedimentary strata, having many folds 

 or corrugations, thereby forming in the Marquette region an irregular trough or 

 basin, which, commencing on the shore of Lake Superior, extends west more than -10 



