362 



Scientific Geology, 



of manganese. Bat on breaking open the mass, we usually find its in- 

 terior to be of a beautiful rose red. This ore has been recently an- 

 alysed by Dr. Thompson, and found to be a bi-silicate of manganese. 

 In the stone walls, a little northeast of the meeting house in Cum- 

 mington, numerous large blocks of this ore are found, which were 

 probably transported thither from the beds above described, by a dilu- 

 vial current from the north : though to reach this spot, they must 

 have passed over a deep valley, through which a branch of Westfield 

 river now runs. 



One never meets with this bisilicate of manganese, which is not 

 coated over with the black oxide. I hence infer that atmospheric 

 agencies produce this conversion. As the bi-silicate is rare in other 

 parts of the world, (indeed Dr. Thompson legards this as a new spe- 

 cies, distinct from the siliceous oxide, on account 6f the double pro- 

 portion of silex which it contains,) its great abundance in Plainfield 

 and Cummington is a matter of joy to mineralogists. 



Connected with the bowlders of this manganese ore in Cumming- 

 ton, I found small but well characterised masses of carbonate of iron. 



The manner in which the above ores of iron and manganese occur 

 in the talcose slate, forbid, it seems to me, the supposition somewhat 

 extensively adopted of late,* that all metallic deposites in solid rocks 

 have resulted from sublimation, through the influence of the heat pro- 

 duced by rocks of igneous origin. For although the layers of the 

 slate are nearly perpendicular, and therefore sublimed matter might 

 easily rise to fill a cavity from beneath, yej; there seems to be no more 

 evidence that these ores were thus introduced, than that the folia of 

 the slate had such an origin ; for the ores as well as the slate are 

 distinctly foliated, and often both are intimately intermixed. What 

 objection is there, in such cases, against regarding metallic deposites 

 as having proceeded from solution and suspension in water, just as we 

 now find iron and manganese forming; and subsequently rendered com- 

 pact and crystalline by the heat of the unstratified rocks ? 



In the beds of steatite that have been described, several minerals of 

 interest occur. Foliated bitter spar exists in almost every one of them; 

 especially at Middlefield, Windsor, Zoar, and Marlborough, Vt. At 

 Middlefield it is sometimes three or four inches diameter, enveloped 

 in masses of delicate green talc ; and is either white or of a salmon col- 

 or, so as to form elegant specimens, as may be seen in the collection 



* See an article by A. L. Necker's Philosophical Magazine, Sept. 1832. p. 225. 



