REPORT OF THE DIRECTOR 1917 87 



lined with the dusty, brownish black dioxide of manganese. Not 

 far from this locality loose boulders of the Rensselaer grit showed 

 dark, circular areas considerably disintegrated but blackened by the 

 oxides of manganese. An occasional vein of quartz and calcite was 

 found in the grit showing the effect of solution on the calcite and the 

 vein walls somewhat darkened by the oxides of manganese. . 



In the vicinity of Spencertown, the grit, slate and schist area 

 through which the Spencertown-Austerlitz state road was recently 

 cut shows a conspicuous veined zone in the grit, consisting of 

 numerous branching quartz veins with conspicuous pink orthoclase 

 and massive chlorite. 



Nearer the village of Spencertown, on the same road, in the slate 

 area, the oxides of manganese are conspicuous by their black stains. 

 The purple and green slates associated with the grits of Canaan as 

 well as those just cited in connection with the grits of Spencertown 

 are doubtless a part of the Ordovician system. 



Mineralogy of the Manganese Belt 



Bog manganese, otherwise known as wad, a variety of psilomelane, 

 is a brownish black amorphous mineral consisting of varying amounts 

 of the oxides of manganese. It is usually earthy but frequently 

 coal-like to submetallic in luster, the variation no doubt signi- 

 fying a transformation to the higher oxides. The occurrence of 

 bog manganese as pure hydrous oxide of manganese is very rare. 

 The common impurities are iron, silica, phosphorus and barium; 

 the silica and phosphorus are objectionable for the metallurgical use 

 of the ore. 



The bog manganese of Columbia county has three habits of 

 occurrence: nodular, aggregates and hardpan cement. The nodular 

 variety is usually found at the surface overlying the other two forms. 

 Nodules somewhat brownish in color and usually enveloped in a 

 whitish clay, in which material they are also embedded, have gener- 

 ally elliptical and subspherical forms with a suggestion of slightly 

 developed botryoidal structure. In size they vary from a pinhead 

 to one-half of an inch in diameter. In dry bogs these nodules occur 

 in the outlets of swamps or in the beds of brooks, the enveloping 

 clay having disappeared, leaving a brownish black surface to the 

 nodule. To this type the name of stream manganese has been 

 applied. 



The second variety of wad, less common than the loose nodular 

 type, was nodular aggregations in a matrix of whitish gray clay 



