448 DALE— CAMBRIAN MANGANESE DEPOSITS OF [April 25, 



We have discussed the nature of the sediments and learned that 

 these terriginous deposits must have been derived from the pre- 

 Cambrian land masses which existed in far greater extent on the 

 east and west of the Cambrian sea than the present areas outlined 

 on page 373. The interbedded character of the manganiferous and 

 argillaceous layers signify alternating conditions of chemical pre- 

 cipitation and mechanical deposition, there being, during the forma- 

 tion of the deposits, times when the Cambrian sea was more man- 

 ganiferous with conditions such that precipitation of manganese 

 carbonate and the oxide was the relatively important feature while, 

 at other times, mechanical deposition of fine muds was the rule. It 

 is more than likely that the greatest portion of the manganese was 

 contributed to the sea in the form of the dissolved bicarbonate by 

 the streams which transported the clastic sediments and that these 

 sediments were not themselves responsible for the major contribu- 

 tion, though undoubtedly the manganese minerals in the muds 

 underwent some solution both during their transit to the sea bottom 

 and during diagenesis. The streams which were responsible for 

 the transportation of the sediments of the manganese deposits and 

 also held, as chief contributors of the manganese, drained the pre- 

 Cambrian land areas above referred to. A modern river like the 

 Ottawa which drains a pre-Cambrian area consisting in great part 

 of Laurentian and Huronian rocks and in all probability not very 

 different from the pre-Cambrian rivers of ancient Newfoundland, 

 has .86 parts per million of manganese in its waters according to 

 an analysis made in 1907 (Shutt, 22: 175). 



Manganese in river water results from the solution of manganif- 

 erous silicates such as pyroxene, olivine, micas, amphiboles, epidotes 

 and chlorites, some of which are the common and essential basic 

 rock-forming minerals of any igneous and metamorphic pre-Cam- 

 brian area. On the decomposition of these elements the manganese 

 is converted into carbonate or oxide and enters into solution, when 

 conditions are favorable, as the bicarbonate, in which form it is 

 carried to the sea, unless oxidized in transit, there to await the 

 further changes into the oxides, MnO, and MnoOg, or the carbonate, 

 MnCOg, depending upon the conditions suggested in the preceding 

 pages. Analyses of some of the pre-Cambrian rocks in the vicinity 



