C. i?. Van Hise — Iron Ores of Michigan. 127 



the iron-bearing formation of the Lower Marquette series 

 would decompose the iron carbonates with which they came in 

 contact arid thus become carbonated. These carbonated waters 

 would then be capable of taking other iron carbonate into solu- 

 tion. What proportion of the original iron carbonate still re- 

 mained in the ore-bearing formation at the beginning of concen- 

 tration is uncertain, but since it is still found in places sheltered 

 from percolating waters, such as the deeper workings of one of 

 the mines and under diorite masses, it is probable that the quan- 

 tity was very considerable. The oxides or carbonates of iron 

 may also have been taken into solution by organic acids. These 

 downward-moving waters would pass through the iron-bearing 

 formation until they came in contact with an impervious 

 substance or else, if passing through the Upper Marquette 

 series, they reached the contact plane between the two series 

 along which they would travel. It is possible that the ore 

 which formed along the contact horizon was contributed in 

 part by the ferruginous materials of the Upper Marquette 

 series, although it is probable that the greater part of the' ore 

 here found came from material of the ore-bearing formation 

 now removed by erosion. After the ore-bearing formation had 

 been leached for a long time, it became as it is now found, 

 very porous along the soap-rock and along the contact plane of 

 the Upper and Lower Marquette series. Here would be 

 carried other oxygen-bearing waters more directly from the 

 surface. The union of these two currents would precipitate 

 the iron oxide. The abundant waters traversing these ore- 

 bearing localities would also slowly dissolve the silica. That 

 this interchange actually does occur is known of the localities 

 in which a detailed examination has been made, as for instance 

 at Republic. It is probable that in the ore-deposits associated 

 with the soap-rocks the removal of silica is due in part to 

 them. Originally diabases, they must have contained alkalies, 

 while analyses of them show at present an almost entire ab- 

 sence of these elements. The alkaline waters produced by 

 their alteration would thus furnish a menstruum capable of 

 taking the silica into solution. This desilicification of the iron- 

 bearing formation by alkaline waters was many years ago sug- 

 gested by Brooks,* for a part of the Marquette district. Ro- 

 mingerf not only made the same suggestion in reference to the 

 Jackson mine, but further held that the siliceous matter re- 

 moved, was replaced by oxide of iron carried by water solutions. 

 The percolating waters which carried material along the 

 readiest paths to form the ore-bodies, and which removed the 

 silica also helped to jasperize the ore bearing formation, i. e. 

 it charged the white silica with oxide of iron and thus red- 

 dened it, although it cannot yet be certainly stated to what 



*Geol. of Michigan, vol. i, p. 134. f Geol. of Michigan, vol. iv, p. 75. 



