74 GEOLOGY OF THE SECOND DISTRICT. 



Origin of Rensselaei-ite. 



Being a mass clearly unstralified, and constantly associated with primitive limestone and 

 serpentine, the theory of its origin must be the same as that of those rocks, which has been 

 very fully stated in the preceding pages. It does not occur in the form of dykes, or present 

 a columnar structure like basalt. Its want of stratification, and its association with rocks of 

 whose igneous origin there can be no doubt, are the principal reasons for the opinions I have 

 adopted. 



Localities, extent, etc. — Tiic largest mass of this rock is in the town of Fowler, St. Law- 

 rence county, partly on the Belmont farm, and extending south or southwest towards Fowler's 

 lake. It occurs in irregular dark and light-colored masses, which are sometimes traversed by 

 veins of satin spar. Quartz, in thin seams, also cuts through, the rock in the neighborhood of 

 the lake. A variety nearly black exists in great abimdance on this farm, in which those veins 

 occur, and which, when it is cut and polished, forms a very ornamental rock. I am unable 

 to determine the value of this rock for mantel pieces, or other similar uses ; as in procuring 

 specimens, and breaking them, they appear to be cracked or shattered. Wlien such masses 

 are exposed to heat, thin cracks or flaws, which were not visible, now appear, and mar to a 

 considerable extent its beauty. The stone is very strong and tough, and will bear heavy 

 blow's without breaking. Some pieces I have placed in a stove with anthracite coal, where 

 they remained several hours without being injured : it becomes slightly harder, more compact, 

 and loses its transparency, and becomes more susceptible of a polish. 



The iron mine in Edwards in the same county, furnishes a handsome white variety of this 

 rock ; it is here associated with serpentine and primitive limestone. Another locality is be- 

 tween Edwards and Russell. Crystallized specimens were found by myself in Canton, in 

 the south part of the town. At Oxbow in Jefferson county, dark radiated masses are abundant, 

 resembling some varieties of anthophyllite. 



On the western side of the Oswcgatchie in Dekalb, and about twenty rods below the bridge, 

 there is a ridge of white rcnsselaerite, in appearance much like tremolite. This ridge extends 

 one hundred rods or more down the river, and in a northeast and southwest direction. In 

 many places it is mixed with quartz, like the same rock at Fowler. There is, therefore, a 

 general similarity running through or connected with the different beds of this mineral. 

 ' Before I close my remarks upon this rock, I should observe that Dr. Thompson considers 

 the substance described as rcnsselaerite, to be anthophyllite ; and it is true that some varie- 

 ties appear externally much like it, still, the crystalline form, which I have been fortunate 

 enough to discover, sets the matter fully at rest. 



