IROX-ORE DEPOSITS OF NEGAUNEE FORMATION. 399 



formation and the Lower Marquette Negaunee formation. As in the cases 

 of (1) and (2), all of the large ore deposits belonging to this third class have 

 at their Ijases soapstone or paint-rock. (PI. XXIX, tig. 2, and PI. XXXIV, 

 fig. 1.) In those cases in whicli the soapstone is within the Negaunee 

 formation it is a modified diabase, or a greenstone mass in conjunction 

 with a dike or dikes. Where the ore deposits are largely or mainly in the 

 Goodrich (juartzite the basement rock may again he a greenstone, but also 

 it may be a layer of sedimentary slate belonging to the Goodrich quartzite. 

 These different classes of rocks are, however, not discriminated b}^ the 

 miners, Ijut are lumped together as soapstone or jjaint-rock. Also, as in 

 the cases of (1) and (2), wherever the deposits are of any considerable 

 size the basement rock is folded into the form of a pitching trough, or else, 

 by a union of a mass of greenstone with a dike, or by a union of either 

 one of these with a sedimentary slate, an impervious pitching trough is 

 formed. Perhaps the most conspicuous example of this is at the Repvxblic 

 mine (PI. XXXIV), but it is scarcely less evident in the other large deposits. 

 However, a few small deposits — chimneys and shoots — of ore occur at the 

 contact of the Negaunee and Islipemiug formations (PI. XXVIII, fig. 3), 

 where no soapstone has been found. As examples of ore deposits which are 

 largely or wholly Avithin the Upper Marquette may be mentioned the Volun- 

 teer, JMichigamme, Champion, and Riverside. These are partly recomposed 

 ores, and differ in appearance from the specular hematite or magnetite of the 

 Lower Marcjuette in having a peculiar gray color and in containing small 

 fragmental particles of quartz and complex fragmental pieces of jasper, and 

 frequently also sericite and chlorite are discovei'ed with the microscope. 



In any of these classes the deposits may be cut into a number of 

 bodies by a combination of greenstone dikes or masses. A deposit which in 

 one part of the mine is continuous, in another part of the mine, hj a grad- 

 ually j)rojecting mass of greenstone which passes into a dike, may be cut 

 into two deposits, and each of these may be again dissevered, so that the 

 deposit may be cut up into a nundier of ore bodies separated by soapstone or 

 paint-rock. (PI. XXVIII, figs. 4-6.) In some cases the ore deposits have a 

 somewhat regular form from level to level, but the shape of the deposit at 

 the next lower level can never be certainly predicted from that of the level 

 above. Horses of "jasper" may appear along the dikes or within an ore 



