364 On the Strontianite of Schoharie, (N. Y.) 



5th. stratum, ten feet in thickness, consists of a dull argillaceous 

 limestone, which resembles, (judging from the specimens sent,) the 

 water-limerock. It is without fossils, but contains the Strontianite, 

 and its associated minerals. 



6th. stratum, five to ten feet in thickness, consists of a compact 

 limestone, and contains Favocites. 



The base of the ledge is strewed over with debris, and the whole 

 formation is bottomed on a siliceous limestone destitute of organic re- 

 mains. 



Without attempting to pronounce upon the geological age of the 

 rocks above enumerated, whose period however, is not encumbered 

 with much doubt, from the fossils mentioned, I shall confine myself 

 to a description of the varieties of the Strontianite, which, on account 

 of the widely different appearances they assume, are with some dif- 

 ficulty recognized. 



The most obvious variety is that in acicular crystals, and massive 

 in long, straight, divergent individuals. It occurs, occupying irregu- 

 lar cavities, from half an inch, to several inches across ; the crystals 

 and fibrous masses being implanted upon a dark blue Calcareous Spar 

 which is granular in large individuals, or crystallized in obscure sca- 

 lene dodecahedra, whose apexes are replaced by three, six, nine or 

 twelve faces. The envelope of Calcareous Spar is sometimes of 

 considerable thickness, and is itself often included within a layer of 

 Heavy Spar, massive in large lamellar individuals, some of which 

 penetrate the Calcareous Spar. But the Strontianite constantly 

 reposes upon the latter mineral. The crystals are often three quar- 

 ters of an inch in length, and from the diameter of a pin to that of 

 a hair. The aggregated, columnar individuals frequently exhibit at 

 the extremity where they diverge most, crystalline faces. Some of 

 these fibrous aggregations are two inches in length, and bear a stri- 

 king resemblance to certain varieties of Arragonite. Minute crys- 

 tals of Iron Pyrites, crystallized in the form of the pentagonal do- 

 decahedron, are scattered here and there through the Strontianite and 

 Calcareous Spar. The color of the Strontianite is white, or slightly 

 tinged with grey or blue ; and it is semi-transparent or translucent. 



A second variety quite different in general appearance from the 

 first, and one which I should imagine, does not occur at the same 

 place with that above described, is massive, indistinctly lamellar, and 

 approaching to impalpable. Color, milk white, rarely with a deli- 

 cate and almost imperceptible shade of green. This variety occurs 



