THE CHEMICAL RELATION OF IRON AND MAN- 

 GANESE IN SEDIMENTARY ROCKS: 



Iron and manganese are frequent constituents of sedimentary 

 rocks, in some places occurring finely disseminated through 

 sandstones and shales, or forming a part of limestones, in other 

 places forming the mass of the deposit in which they occur. 

 They are both derived primarily from similar, and often from the 

 same sources, and are in many respects alike in their chemical 

 behavior in nature. For these reasons it is to be expected that 

 they would frequently, if not generally, be deposited in intimate 

 association. Such is found to be the case, and iron and mangan- 

 ese are often closely associated in the same deposits. Very 

 often, however, iron and manganese deposits occur close together, 

 but distinctly separated, while sometimes extensive deposits of 

 iron, and less commonly of manganese, occur with little or almost 

 no association with each other. 



It is the object of the present paper to discuss the agencies 

 which are instrumental in causing these substances to be depos- 

 ited sometimes together and at other times separately. The 

 subject is of interest as showing how slight differences in the 

 chemical behavior of their salts rnay cause the almost complete 

 separation of metals once intimately associated. 



THE CONNECTION OF IRON AND MANGANESE IN NATURE. 



A few words concerning the relation of manganese to iron in 

 nature will perhaps make the following discussion clearer. One 

 of the most common modes of occurrence of manganese is with 

 iron, though extensive deposits containing manganese more or 

 less free from iron often occur. When associated with iron, 

 manganese occurs with it in various ways. Sometimes the two are 

 intimately mixed, so that they have the appearance of a homoge- 



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