84 ROYAL SOCIETY OF CANADA 



ditions causiug the alternate precipitation ot silica and iron should have 

 heen very widespread in two continents, and absent in all other regions ; 

 and it may be that they have simply been over-looked in other parts of 

 the world. 



The mode of formation of the banded iron-silica rocks is by no 

 means finally settled. Some American geologists think them derivations 

 from an original siliceous siderite, rearranged by heat, circulating water, 

 and certain reagents; but in a great many of the outcrops in Ontario, 

 and, T believe, in all of the outcrops described in South Africa, siderite U 

 absent. It is possible, of course, that in these cases the siderite has been 

 completely rearranged, but it seems more probable that the stratified 

 looking iron ore and silica were originally deposited on a sea bottom, 

 though perhaps not in their present form. The character of that sea 

 must have been very different from any known at present, and one is 

 tempted to speculate as to solvents and précipitants which could 

 act over hundreds of miles of sea bottom, piling up beds of crystalline 

 silica and magnetite or hematite still hundreds of feet thick after all 

 the erosion they have undergone. This, however, would lead too far. 



South Africa is fairly well provided Math coal, and a time may come 

 when iron will be produced in the different colonies. Judging from 

 American iron mining regions large and rich ore deposits of secondary 

 origin may be looked for wherever the lean iron bearing rocks have been 

 enclosed in basins permitting a slow concentration. That such deposits 

 of economic importance will be found in South x4.frica seems very 

 probable. 



