72 GEOLOGY OF THE SECOND DISTRICT. 



in a few instances, as at Pitcaim and Fowler. Asbestus, in beautiful silky veins, is abundant 

 at Port Henry. Talc, so commonly connected with the beds of serpentine in Massachusetts, 

 does not occur so frequently in connection with the serpentine of the northern counties. 

 Neitlicr do the minerals of the limestone, as brucite, augite and spinelle, ever occur in the 

 serpentine. 



Beautiful satin spar is found in the serpentine at Pifcairn, and copper-colored mica at 

 Gouverncur. The fact, however, most interesting in relation to the serpentine, is of a nega- 

 tive character : that those substances so common, or in fact characteristic in the serpentines 

 of other places, are entirely absent here ; a fact which goes far towards confirming the 

 opinion already expressed, that they are of different ages, or belong to different periods. The 

 magnetic oxide of iron does not occur in New-York in the same «tate of oxidation as at Troy 

 in Vermont, but it is not improbable that the specular ore takes the place of the magnetic ; 

 if so, the association of serpentine with the axide of iron may be considered as a constant 

 fact. The change in the oxidation of the magnetic oxide into the peroxide, is not to be lost 

 sight of ; for the only fact of importance is the association of an oxide of iron, its state of 

 oxidation being merely an accidental circumstance. 



At Middleficld, Mass., a metallic substance like chromite of iron, is diffused very generally 

 through the rock. Some of the particles are probably the magnetic oxide, and others the 

 chromite. In 1820, dodecahedral crystals of the magnetic oxide in the serpentine were dis- 

 covered by myself, associated with massive chromite of iron and pseudomorphic crystals of 

 steatite. 



5. Rensselaerite. 



In placing this substance among the rocks of New-York, I have been governed by the prin- 

 ciple, that all masses which exist independent of veins and disseminated particles, or crystals, 

 should be ranked with the rocks proper, though they may be quite limited in extent, and con- 

 fined, so far as discoveries have been made, to the northern counties of New-York. Rens- 

 selaerite, though not strictly a new substance, was separated from steatite, or soapstone, in 

 the report for 1 837.* It had been employed under that name for many years, for the manu- 

 facture of inkstands, and several other small domestic articles. Their use, however, had been 

 confined mostly to a small section of country ; and in consequence of being cut, and imper- 

 fectly polished, they appeared much like the common steatite, which was in use for similar 

 purposes. Though there is a resemblance, yet, in fresh quarried specimens, the rensselaerite 

 docs not exhibit that flaky appearance so characteristic of steatite ; and it required only a 

 slight examination, to discover that it diflfered materially from soapstone. 



Considered as a mineral species, rensselaerite possesses the following properties : Hard- 

 ness equals .3.5 to 4.0, or between calcareous and fluor spar : specific gravity, 2.874. The 

 crystalline form under which it appears, is an oblique rhombic prism, of the same measure- 



' Apppnilix to tlio Report of the Second Geological Pislrict, p. 154. 



