I9I4.] CONCEPTION AND TRINITY BAYS, NEWFOUNDLAND. 443 



,to point clearly to the conclusion that the deposits are essentially of 

 sedimentary origin, rather than products of a later ground water or 

 weathering concentration. But beyond this conclusion, there is 

 room for great diversity of opinion. 



Two questions present themselves at the outset of the inquiry: 

 Was the manganese deposited contemporaneously with the clastic 

 sediments in its present degree of concentration? Or, was it some- 

 what disseminated through the muds and subsequently concentrated 

 by diagenetic agents? While the first of these alternatives is held 

 by the writer to be highly probable, no positive and final answer can 

 be given to these and to many other questions raised by a study of 

 the problem of genesis, although various suggestions are presented 

 in the following pages. 



Manganese exists in sea-water and has been noted by For- 

 chhammer and by Dieulafait (6: 718) but not in sufficiently con- 

 centrated form to produce deposits similar to those under considera- 

 tion. Murray and Irvine (19: 735) found that the red muds of 

 the mid-Pacific and Indian Oceans, which were made up in large 

 parts of basic vitreous volcanic minerals, were responsible for the 

 large amounts of pulverulent and nodular ferromanganese. These 

 nodules consist on the average of 29 per cent, of MnOg and 21 per 

 cent, of FcgOg with the remainder largely clayey material. The 

 basic glasses contain the only important primary manganese-bearing 

 minerals in the ocean and the manganese is reported by Murray and 

 Irvine to have undergone conversion into the soluble bicarbonate 

 which upon reaching oxygenated surface waters, is decomposed with 

 precipitation of the dioxide. The particles of MnO, falling to the 

 bottom gather upon various objects which serve as nuclei for con- 

 cretions, or the nuclei themselves may have been the cause for the 

 precipitation. Murray and Hjort (17: 192) in this connection 

 say: 



" It should be noted that these oxides need by no means necessarily assume 

 a concretionary form. They are very commonly found as thin incrustations 

 on granular and fragmentary objects. Furthermore many, if not most, of 

 the pelagic clays contain intimate admixtures of finely divided brown man- 

 ganese and occasionally of limonitic iron. Here the supersaturation would 

 seem to have been so high as to transgress the metastable limit, whereupon 

 the oxides have precipitated themselves without the intervention of nuclei ; 

 they certainly must have been precipitated from solution." 



