EARLE, INTERBEDDED IRON ORE DEPOSITS 117 



In Birmingham and Attalla, Alabama ; in Clinton, New York, and in 

 many other places, the same conditions prevail, and hard ore under- 

 ground mining has largely superseded the soft ore open-cuts. 



Deep borings, in some cases nearly 3,000 feet in depth and several 

 miles from the present workings, have brought to light conditions un- 

 known in former times. Genetic theories, advanced originally from a 

 study of outcrops and open-cut mines, undoubtedly would have been 

 different, had the present data been available at the time. Yet with all 

 the data accessible at the present time and much literature within reach, 

 the question of the genesis of interbedded Paleozoic iron ores, and more 

 particularly the Clinton ores, is still in controversy. Men of established 

 reputation and wide experience adhere to theories sharply at variance 

 with one another. At least two and possibly three such theories are still 

 advanced and have the active support of men prominent in the mining 

 and geological world. 



The practical importance of an accurate knowledge of the origin of 

 these ores must not be overlooked. Upon such knowledge depends the 

 interpretation of conditions underground below the present zone of 

 mining, the depth to which the ore may be expected to go and the con- 

 tinuance or change of richness of the ores. 



It has been the purpose of the writer to include in this paper a brief 

 reWew of former theories and to discuss these theories in relation to re- 

 cent field and laboratory developments, showing where they fail to meet 

 certain conditions now known to exist and therefore must to some extent 

 be altered or superseded. 



Further, the paper proposes and elaborates a theory of genesis which 

 the writer has worked out in the field and laboratory and which, in order 

 to separate from other theories and to avoid confusion, he calls the "Arte- 

 sian Replacement Theory." 



In brief, the writer attempts to maintain the following thesis : that the 

 Paleozoic interbedded iron ores of eastern North America, and more par- 

 ticularlv the so-called Clinton ores, are replacements of porous strata of 

 ordinary mechanical sediments by iron oxide, the agency being ferrugi- 

 nous waters acting under artesian conditions. 



Acknowledgments 



The writer wishes to acknowledge the criticisms, suggestions and as- 

 sistance given by Prof. J. Edmund Woodman, Dr. Albert B. Pacini, 

 Dr. Augustus Pacini, Prof. C. H. Smyth, Jr., S. W. McCallie, E. C. 

 Eckel, E. P. Burchard, Chas. A. Borst, Dr. E. A. Smith, Dr. E. 0. 



