Oxide of Manganese. 



123 



meets with water containing carbonic acid, by which it is dissolved. 

 Once dissolved, it is readily transported to ponds and swamps, and 

 there deposited by the evaporation of the water. In the region above 

 referred to, this process may be witnessed in all its stages. By break- 

 ing the rock we find the sulphuret unchanged; while the surface is 

 coated over with the oxide, sulphate, and carbonate. The soil, also, 

 to a considerable depth, exhibits very strikingly the color of iron 

 rust; and in the low grounds the bog ore is abundant. 



Probably a similar theory will apply to the production of this ore 

 in other parts of the State ; though I know of no spot where the 

 process is so obvious as in Worcester County. Indeed, the fact that 

 very many of our bog ore deposites are buried several feet deep by 

 soil, and occur on dry ground, shows that in those places the process 

 of its formation has long since ceased. In several ponds in the south- 

 east part of the State, it is said, however, that it is forming rapidly. 



Since iron is a mineralizer of organic substances, we might expect 

 to find organic remains in bog ore. In that of Massachusetts, I have 

 noticed only vegetable relics. In New Braintree the culms, spikes, 

 and spikelets of grasses — mostly of carex — are common. The 

 spikes and spikelets especially, are very distinct and perfect. (No. 19) 

 Even the natural color of the fruit is sometimes preserved ; and to 

 appearance it seems to be unaltered ; but examination shows the 

 whole to be only iron ore. 



Oxide of Manganese. 



I know not why geologists have omitted this substance in enumer- 

 ating alluvial deposites. For it seems to have as good claims to be 

 regarded alluvial, as bog ore and peat. I refer particularly to the 

 hydrated oxide, or black wad ; which is ordinarily a mixture of man- 

 ganese, iron, and clay. This is certainly produced daily by a process 

 analogous to that which forms bog ore ; that is, the decomposition of 

 rocks containing manganese, exposes that metal to be washed by 

 water into cavities on the surface of the earth, where it either incrusts 

 other substances, or forms a separate deposite. Instances of this in- 

 crustation may be seen every where in the primary region west of 

 Connecticut river ; and examples of such deposition I have observed 

 in Leverett, Whately, and Conway. These deposites are sometimes 

 a foot in thickness, and occur in low places, covered only by a few 

 inches of soil. 



