[COLEMAN] SOUTH AFRICAN IRON FORMATIONS S 8 



seems good evidence in writings of the South African geologists that 

 rocks of the kind belong to more than one age, but that all are relatively 

 ancient. 



Unfortunately fossils have never been found in South Africa in 

 rocks beneath the Devonian, so that lower rocks can be classified as to 

 age only by stratigraphical or lithological methods. 



The 'Griqua Town series of northern Cape Colony and the Campbell 

 Tîand series, into which it passes down^^-ards, are followed by two 

 or three lower series of rocks, separated from one another by uncon- 

 formi^; while above the Griqua Town series the Pre-Cape rocks and 

 the Table Mountain series intervene before the Bokkeveld series is 

 reached, from which Devonian fossils are known. 



As the Keewatin rocks, containing our most important iron forma- 

 tion, are the oldest known rocks of their region and have nothing be- 

 neath except the La.urentian ernptives which have burst through them, 

 it appears that our Helen Iron Formation, for instance, must be more 

 ancient than any of the South African iron bearing rocks. However, 

 banded silica with iron ore occurs also in higher formations in America, 

 especially the Animikie, or Upper Huronian of the latest classification, 

 with no less than three important breaks between it and the Keewatin; 

 so that the Animikie may be of somewhat the same age as the South 

 African iron bearing formations. Since banded silica with iron ore 

 occurs at more than one horizon in South Africa, some outcrops of these 

 rocks, as in the Barberton series of Natal or the occurrence near Salis- 

 huTj in Ehodesia,, may be much lower down in the geological scale than 

 those of the Prieska region, and may represent our Keewatin Iron 

 Formation, or the Lower Huronian, which comes next in order above it. 



Wli ether the South African and the N"orth American rocks contain- 

 ing interbanded silica and iron ore are of the same age or not, 

 they clearly indicate similar conditions of deposit in very 

 ancient times and in very different parts of the globe. Why these curi- 

 ous and important types of rock, consisting essentially of silica and iron, 

 should have formed only in ancient seas (Pre-Silurian at least), and not 

 in later times, remains mysterious; and for the present it may be suffi- 

 cient to call attention to the fact that our own Pre-Cambrian formations 

 of banded silica and iron ore which have attracted so much attention 

 and speculation, are by no means unique, but are repeated, on an even 

 larger scale in the southern hemisphere. 



It is rather singular that iron-silica rocks of a banded character 

 liave not been reported from Europe and otlier regions, when they are 

 found occupying hundreds of square miles among the more ancient rocks 

 of Xorth America and South Africa. One can hardly imagine that con- 



