I96 NEW YORK STATE MUSEUM 



So, in the case of the Clinton ores, even were it proved that they 

 resulted from the alteration of the silicate, the fact that this silicate 

 is not glauconite would, as shown above, leave its origin or, in other 

 words, the nature of the first concentration of the iron, unsettled. 



For ores of the Clinton type, the problem of the genetic relations 

 of oxides, silicates and other compounds of iron has been most 

 elaborately treated by Cayeux 1 in a magnificent monograph of which, 

 unfortunately, only the first part is as yet available. The iron 

 silicate is regarded as the usual stage intermediate between the car- 

 bonate and the oxide, the genetic sequence being (1) calcium car- 

 bonate, (2) iron carbonate, (3) iron silicate, (4) iron oxide, the last 

 three compounds, in the order named, being regarded as replacing 

 calcium carbonate. 



The importance of these conclusions can not be doubted and, 

 throughout the foregoing discussion, they have been kept constantly 

 in mind. But at the same time the actual geological conditions 

 have been taken as the key to the solution of the genetic problem 

 and these have indicated a relatively minor role for the secondary 

 processes. Cayeux, on the other hand, regards these processes as 

 the essential cause of ore formation, starting with the replacement 

 of calcium carbonate by iron carbonate. 



As the data at present under consideration shed no important 

 light upon the possible formation of the Clinton ores by the replace- 

 ment of limestone, it would be futile to repeat, here, the discussions 

 of this phase of the problem which have been published in earlier 

 papers. 



In general, it may be said that the writer's conclusion, that the 

 ores are primary, is based much more upon their larger geological 

 relations than upon any minute details of structure and composition. 

 Important though the latter be, they are often capable, as appears 

 above, of diverse interpretation; while the larger features of dis- 

 tribution, relation to other rocks, limitation to certain horizons, 

 shape of deposits, continuity in depth etc., to the writer, seem to 

 admit of but one interpretation — that of deposition of the iron 

 in each bed before the deposition of the overlying bed, in other 

 words, primary deposition. 



Replacement of calcium carbonate, when it has occurred, is 

 regarded as of the contemporaneous type, taking place during the 

 accumulation of the calcareous materials on the sea bottom; and, if 



1 Cayeux, L., Les Minerals de Fer Oolithque de France, Fasc. I, Minerals de 

 Fer Primaires, Paris, 1909. 



