382 



DALE— CAMBRIAN MANGANESE DEPOSITS OF [April 25, 



tant nodule. The nodules, measuring as much as 6 inches in diam- 

 eter, consist largely of argillaceous material, jaspery concentric 

 bands, blades of barite, pyrite and some disseminated manganiferous 

 and ferruginous carbonate minerals which are surrounded by dark 

 areas. These latter are probably manganese oxide zones due to the 

 alteration of a manganiferous carbonate. 



Under magnification these nodular portions are roughly con- 

 centric and laminated in structure, with laminations red and green 

 in color, and of fine and coarse grain. An oolitic structure, but with 

 the spherules poorly formed, is found in combination with the 

 banded structure. Calcite occurs as somewhat elongated crystals 

 and is the dominant mineral. Wherever the calcite presents the 

 pecuhar elliptical and circular shapes mentioned on page — , an 

 organic origin is immediately suggested (Fig. 5 and 6, Shde 254). 



Fig. 5. Microphotograph of limestone, 219 Bsd; slide 254; enlarged 22 

 diam. a, elliptical calcite aggregations; b, chlorite; c, hyolithes. 



Quartz is found as irregular grains and aggregations. Barite occurs 

 only sparingly. Among the opaque minerals, pyrite sometimes alter- 



