770 T. C. BROWN OOLITES AND OOLITIC TEXTURE 



with nuclei of sand grains or some foreign material. These oolites are 

 in almost every case mingled or associated with fossils or fragments of 

 fossils composed of the same material, namely, iron oxide mingled with a 

 certain amount of amorphous silica. Both oolites and fossils are, as a 

 rule, imbedded in a matrix of calcium carbonate, sometimes in a granu- 

 lar condition and sometimes in the form of rhombohedral crystals. If 

 these fossils and oolites were composed of calcium carbonate we would 

 have an association exactly similar to that which is forming today around 

 the Eed Sea and certain deep-sea islands like the Bahamas and Ber- 

 mudas, or like that which accumulated during the Pleistocene around 

 the Florida Keys. 



The fossils certainly were not originally formed of iron oxide and 

 silica, and the oolites have just as certainly undergone the same changes 

 and passed through the same history as the fossils. Evidently both were 

 calcium carbonate originally, and they have been changed by silica-bear- 

 ing ferruginous solutions and molecular replacement to the iron oxide 

 and silica of which they are now composed. The process of replacement 

 was exactly the same in general outline as that described for the replace- 

 ment of the State College siliceous oolites. It differed from that process 

 chiefly in that here ferruginous salts were dominant in the solutions, 

 with silica playing a subordinate part, while in the siliceous oolite re- 

 placement silica was the dominant material in solution and ferruginous 

 salts were present in an amount only sufficient to give a faint color to 

 the concentric layers or occasionall}^ form a coating around the nuclear 

 sand grain. 



Smyth and others have considered these Clinton oolitic ores direct 

 chemical precipitates from ferruginous solutions, and they have based 

 their argument on Newberry's statement that similar ores are now form- 

 ing in many Swedish lakes.** The conditions under which these Swedish 

 lake ores are accumulating are certainly far from comparable with those 

 under which the Clinton ores accumulated; furthermore, the recent de- 

 scriptions of these Swedish lake ores hardly suggest that they could ever 

 become ores like those of the Clinton beds.*^ 



Smyth has undoubtedly presented the strongest arguments in favor of 

 the original deposition of the iron ore as an oolitic iron oxide. Those 

 arguments which have a direct bearing on the present discussion may 

 be summarized as follows: (1) "How is it possible for an iron-bearing 



** J. S. Newberry : Genesis of the ores of iron. School of Mines Quarterly, November, 

 1880. 



^ For descriptions of the Swedish lake ores see J. A. Philips and Henry Louis : A 

 treatise on ore deposits, 1896, p. 538 ; also R. Beck : The nature of ore deposits (W. H. 

 Weed), vol. i, 1905, pp. 100-101. 



