REPORT OF THE DIRECTOR I917 19/ 



the replacement hypothesis is given this limitation, not only are the 

 chief evidences against it removed but, as clearly indicated in all pre- 

 vious discussions by the writer, its acceptance, for certain phases of 

 the ore, is inevitable. 



Subsequent relative enrichment of ores, by the leaching out of 

 calcium carbonate by ground waters, is clearly recognized, but that 

 the same waters actually brought in the iron and replaced the 

 carbonate, thus converting limestone into iron ore, is not accepted 

 as a factor of any considerable importance in the genetic process. 



Though not bearing directly upon the foregoing discussion, a few 

 words may be added with regard to the various minor constituents 

 determined in Doctor Morley's analyses of which no mention has 

 been made. 



Manganese, as might be expected, has undergone some con- 

 centration as compared with its average amount in the lithosphere, 

 the latter being, according to Clarke, 1 0.05 per cent while the mean 

 of the six specimens analysed is 0.47 per cent. The range is from 

 0.13 per cent to 1.06 per cent, the variation being exceedingly irregular 

 and independent of the iron. Indeed, the minimum amount of 

 manganese and the maximum amount of iron occur in the same 

 specimen, the oolitic ore, no. 5. 



The small amount of K 2 0, particularly in nos. 1 and 2, has already 

 been referred to as indicating that the green silicate can not be 

 regarded as glauconite. Beyond this, the alkalies have no particular 

 significance but their accurate determination in rocks of this char- 

 acter is unusual and affords data that may prove valuable in other 

 connections. • 



Sulphur is, practically, all present as pyrite, a mineral of quite 

 varying distribution in the rocks and one whose genetic relations 

 are of much interest, in themselves, but not sufficiently worked 

 out to shed real light on the ore problem. In general, it may be 

 said that the pyrite appears to be for the most part of distinctly 

 secondary origin. 



Ti0 2 , averaging for the six analyses 0.165 per cent, is considerably 

 reduced, not only as compared with its amount in the lithosphere 

 as a whole, 0.77 per cent, but also as compared with sedimentary 

 rocks in general, the amount falling between that of sandstones 

 and of limestones, and far below that of shales. In view of the 

 known geochemical behavior of titanium compounds, this is what 



Clarke, F. W., The Data of Geochemistry; U. S. Geol. Survey Bui. 616, 



p. 22, I916. 



