440 DALE— CAMBRIAN MANGANESE DEPOSITS OF [April 25, 



is quite probable that others of the manganif erous beds analysed are 

 phosphatic. 



Barite (BaS04) is probably more common than the analyses 

 indicate and is probably included with the SiO, and CaO. It is a 

 conspicuous associate of these deposits, as has been found to be 

 the case with manganese deposits in other parts of the world. The 

 chemical reason for this association of two very different chemic- 

 ally-acting elements, as well as the genesis of barite are discussed 

 on pages 451-453- 



AI2O3, though not as abundant in the important manganiferous 

 beds as in a typical shale, which that of Anal. G approximates, is of 

 sufficient abundance to connect these deposits with the argillaceous 

 sediments. CaO and MgO are in greater amounts than in ordi- 

 nary shales, giving the deposits a calcareous or dolomitic character. 



From a study of the mineral percentage composition of the 

 samples analysed, the manganese rocks are found to be essentially 

 calcareous or dolomitic argillaceous carbonates and oxides or car- 

 bonate-oxides of manganese, with hematite, barite, and tri-calcium 

 phosphate as the chief accessories. 



The following iron determinations of the green and red shales 

 of the manganese zone at Manuels, Conception Bay, show some 

 interesting results. 



FeO. Fe203. 



Red shale, 210 A 4 4.58 3.86 



Green shale, 219 A 3 3.66 3.12 



Red band, 219 A 7 1.69 4.25 



Green band, 219 A 7 3.21 3.36 



It is quite evident from the above analyses that the color in the 

 green shale A 3 and in the green band A 7 is not due entirely to the 

 ferrous iron as we find considerable FcoOg in both. In the green 

 shale, A 3, there is an excess of .54 per cent, of FeO over the FcgOg, 

 while in the green band, which is manganiferous, there is an excess 

 of .15 per cent, of the ferric oxide (hematite) over the ferrous 

 oxide. In the green band we should expect a masking of the green 

 by hematite inasmuch as there is such an excess of the ferric over 

 the ferrous. Thin sections of this band and the green shale reveal 

 some hematite but in very inconsiderable amounts ; not enough, at 



