370 THE JOURNAL OF GEOLOGY. 



ganese frequently found disseminated through shales, sandstones 

 etc. In these rocks they usually form a small but often a very 

 important part, for in many cases the iron and manganese is taken 

 into solution from the rocks and redeposited by a process of re- 

 placement with carbonate of lime in neighboring beds of 

 limestone, or more rarely by replacement with other rocks, thus 

 giving rise to important ore deposits. The question of the asso- 

 ciation and separation of the iron and manganese in these replace- 

 ment deposits depends on a number of conditions, the princi- 

 pal of which are, just as in the class of deposits that has been dis- 

 cussed, the conditions during deposition and the forms in which 

 the iron and manganese are precipitated. The processes by which 

 association and separation occur in replacement deposits dif- 

 fer somewhat in detail from the processes just discussed, but are 

 based on the same principles. 



Many of the iron and manganese deposits of the Appalachian 

 region are supposed by many to be replacement deposits.. N. S. 

 Shaler' in 1877 suggested that some of the iron deposits of 

 Kentucky and Ohio were formed by the solution of iron from 

 certain rocks, and its deposition in the form of carbonates by 

 replacement with underlying limestone. Subsequently it was 

 changed by oxidation to brown hematite. A notable case 

 of replacement has also been shown by R. D. Irving and 

 C. R. Van Hise ^ in the iron deposits of the Penokee series of 

 Michigan and Wisconsin. Here the ore is supposed to be 

 partly a replacement of chert in a trough between quartzite 

 and igneous rocks. The solution that contained the iron 

 was derived from strata in the same series of rocks in which 

 the iron was re-deposited and contained a certain amount 

 of manganese. It is shown how the iron and manganese were 

 more or less separated in the replacement process and that the 

 separation was due to the difference in the oxidability of the car- 

 bonates as explained on page 363. 



R. A. F. Penrose, Jr. 



MCentucky Geo!. Survey, Report of Progress, Vol. III., New Series, 1877, p. 164. 

 - U. S. Geo]. Survey, Tenth Annual Report, 1888-1889, Vol. I., pp. 409-422. 



