GEOLOGICAL EXPLOITATIONS AND LITERATUKE— 1892. 131 



(likes of " fjToenstonc," wliicli were orif^inully, in inost cjises, diabase. In 

 their present <'i)iiiliti<)U tliev eonsist of (lii)rites, chlorite-scliists, talc-schists, 

 and other siniihir rocks which are known h)cally as " soapstones," "paint 

 rock," etc. 



The rocks overlvinjj;- the ores are the congh)inerates and quartzites at 

 the base of the Upper series. The rocks occupy a g-reat syncUnal folil, 

 which in some places is corrugated into minor folds. 



After thus outlining the general features of the lower iron formation, 

 the author proceeds to discuss the mode of origin of the ores. He clas- 

 sifies the deposits as follows: (1) Those at the contact of the quartzite- 

 conglomerate and tlie ore-bearing formation ; (2) those resting upon soap- 

 rock, which grades into massive diorite; (3) those resting upon soap-rock 

 dikes cutting the formation; (4) those interbedded in the jaspers and cherts. 



Deposits of the first kind consist usually of specular or magnetic ore. 

 They occur either within the underlying jasper-ore formation or within the 

 basal layers of the conglomerate. In the latter case they are genuine 

 detrital concentrations. Those deposits within the jasper, but at the contact 

 of this with the conglomerate, are found usually where the former rock is 

 shattered, or sharjily folded, or where cut by dikes. The jasper often 

 passes into the ore gradualh'. 



lu following a. jasper baud toward the ore it was found that instead of remaining 

 solid it becomes porous and frequently contains considerable cavities. These spaces 

 m the transition zone are lined with crystalline ore. In passing on toward the ore 

 deposit more and more of the silica is found to have been removed, and the ore has 

 .eplaced it to a corresponding degree. An examination at many localities led to the 

 conclusion that the transition from the banded ore and jasper to the ore takes place 

 as a consequence of the removal of silica and the substitution of iron oxide. Often 

 m these cases the fine grained jiart of the ore is that of the original rock, while the 

 coarser material is the secondary infiltration. (P. 121.) 



The deposits of the second class comprise manv of the soft ores and 

 some of the hard ores. In either case the ore body follows along the con- 

 tact plane between tlie impervious "soapstone" and the unchanged jasper. 



In deposits of the third class the ore, which is usually soft, nuxx lie 

 upon both sides of a vertical dike. When the dike is inclined at a high 

 angle the ore lies on its upper side only. In the troughs formed by inter- 



