Sbction IV., 1906. [ ^^ ] Trans. R. S. C. 



VI, — South African Iron Formations. 



B}^ A. P. COLEMAX. 

 (Read May 23rd, 1906.) 



While in South Africa with the British Association last summer 

 two interesting localities -^-ere visited where silica interbanded with iron 

 ore is well displayed, and having come directly from the Keewatin Iron 

 Formation north of Lake Superior, I could not help being deeply im- 

 pressed with the resemblance of these formations in such widely 

 separated localities. 



Our Canadian iron ranges in northern Ontario are always asso- 

 ciated with the banded rocks just mentioned, red jasper with darker 

 bands of hematite or magnetite, or white or gray granular silica alter- 

 rating with darker bands containing magnetite; which are found as 

 ridges in the Keewatin of Ontario, as well as in the United 

 States to the west and south of Lake Superior. Since many of the 

 great ore bodies of that famous iron region have been formed by the 

 secondary concentration of hematite or limonite from lean rocks of the 

 kind described, it is of interest to compare the iron formations of the 

 two regions. 



South African geologists themselves have pointed out the resem- 

 blance, so that no originality can be claimed by the present writer in 

 calling attention to it; but a direct comparison of some of the South 

 African rocks and their geological associations with the similar rocks 

 of the Lake Superior region may be of value from the scientific side, 

 and may give hints as to the probability of workable bodies of iron ore 

 occurring in various colonies in South Africa. 



The first examples observed of banded silica resembling the iron 

 formation were found as boulders and pebbles in the Dwyka conglom- 

 erate near Matjesfontein in the Karoo (Cape Colony) ; somewhat as 

 the Canadian iron formation is found as pebbles in the basal Huronian 

 conglomerate. Their original home could not be determined with cer- 

 tainty, however. 



The next locality was on Hospital Hill, a well-known suburb of 

 Johannesburg in the Transvaal. Here beautifullv banded specimens 

 may be found, sometimes straight and even, but often as much folded 

 and contorted as in our own Keewatin rocks. The banding is of white, 

 brownish and reddish silica, distinctly granular, but very fine grained, 

 with somewhat crystalline hematite and a little ma.gnetite. 



Sec. IV., 1906. 4. 



