396 THE MARQUETTE IKON-BEARING DISTRICT. 



However, a close examination of numeroiis localities shows that the 

 greenstone changes by minute gi-adations into the schistose soapstone, and 

 this into the paint-rock, and that therefoi-e these phases are merely parts of 

 the greenstone which have been profoundly altered by mashing and leaching 

 processes and which have been strongly impregnated by iron oxide. Many 

 of the thinner dikes are wholly changed to paint-rock or soapstone, or to 

 the two combined. The larger number of these troughs are found along the 

 western third of the Ishpeming-Negaunee area. By examining the maps 

 (Atlas Sheets IV, XXV, and XXVIII), the masses of greenstone may be 

 seen partly inclosing several westAvard-opening bays, which are occupied by 

 the iron formation. (See also PI. XIII.) Conspicuous among these are the 

 Ishpeming basin, the northern Lake Angeline basin, the southern Lake 

 Angeline basin, and the Salisbury basin. In each of these cases the green- 

 stone forms an amphitheater about the rocks of the iron-bearing fonnation. 

 Areas of iron formation open out to the west into the main area, and thus 

 the troughs have a westward pitch. In the case of Lake Angeline, an 

 east-and-west dike cuts across the basin south of the center, and this, com- 

 bined with the greenstone bluffs to the north and to the south, forms two 

 westward-pitching troughs. The northernmost of these has the greatest 

 ore deposits of the Marquette district, containing many millions of tons 

 of ore. 



(3) The hard-ore bodies, mainly specular hematite, but in some 

 deposits including much magnetite, occur, as has been said, at the top 

 of the iron-bearing formation, immediately below the Goodiich quartzite 

 and within the lower horizons of the Goodrich quartzite. (Pis. XVI, 

 XXVIII, figs. 1, 3, and 7, and XXIX, fig. 2.) As typical examples of 

 mines of this class may be mentioned the Jackson mine, the Lake Superior 

 Specular, the Volunteer, the Michigamme, the Riverside, the Champion, 

 the Republic, and the Barnum. Also, as interesting deposits, giving the 

 history of the ore, may be mentioned the Kloman and the Goodrich. In 

 all of these deposits the associated rock of the iron formation is jaspilite or 

 griinerite-magnetite-schist, usually the former. These ore deposits, bridg- 

 ing two different geological series, can not be separated in description, for 

 frequently they weld together the Upper Marquette Goodrich quartzite 



