404 THE MAKQUETTE IllON BEAIMNG 1)I8TKICT. 



quartz, reddening them and changing the material from white chert to red 

 jaspei-. In some places this jasperization extended deeper than in others, 

 and, as already said, at other places it alDruptly stopped at an impervious 

 mass of soaprock. 



One or two questions remain to be considered: first, why the ore is 

 so frequently hard and specular along the contact horizon or in the jasper 

 and is usually soft within the ferruginous chert; second, why the magnet- 

 ites, when present, occur at tlie contact horizon. 



An examination of the jasper associated with the hard ores shows tnat 

 crystallized hematite and magnetite occur in many cavities formed by the 

 removal of silica. In such geodal cavities these materials were deposited 

 in a granular crystalline condition. In the continuation of the process the 

 silica was wholly removed and its place taken by the crystalline hematite 

 and magnetite. The adjacent jasper also shows numerous cracks and 

 fissures filled with hematite or magnetite. The manner in which these 

 veins of coarser crystallized material frequently cut across the finer- 

 grained substances, which represent the iron oxides j^resent before the 

 final concentration of the ore, shows conclusively that they are secondary 

 infiltrations later than the last orogenic movement. The formation of the 

 coarsely crystalline granular liematite and magnetite thus appears to have 

 been connected with the abundance of iron-bearing solutions along the 

 contact plane. 



In many places, however, the hard ores are of the brilliant micaceous 

 or specular variety. This is sometimes called slate ore. In the liand 

 specimen of jaspilite, composed of minute alternating layers of liematite 

 and quartz, where the folding has been severe micaceous ore is found 

 between the rigid bands of quartz. Along the ferruginous laminae is seen 

 all the ev-ideuce of slickeusides. The micaceous character of the ore is 

 in this case plaiidy due to the accommodation and consequent shearing 

 which took place between the layers. 



The micaceous ore from the large deposits, as first suggested by 

 Pumpellv, gives the same evidence of shearing. ^Vlien it is remembered 

 that in the folding oi thick formations readjustments must occur, it is natural 

 to suppose that they took place more largely at the contact between the 



