96 NEW YORK STATE MUSEUM 



from other sources is perhaps the least conclusive part of the 

 explanation as given. This entails a rather unusual chemical com- 

 position that is hardly in conformaty with the character of the 

 limestones in the district. As a rule they are not particularly sili- 

 cious or impure. An alternative to that view, which would seem 

 equally probable in the circumstances, may be found in the intro- 

 duction of silica and magnesia along certain beds by underground 

 circulations after the limestones were formed. 



It is of interest to note that a belt of metallic ores is found in 

 the same limestones on the footwall side of the talc beds. The 

 ores include zinc blende, pyrite and hematite and occur at intervals 

 from Sylvia lake on the southwest to beyond Talcville. They have 

 undoubtedly been deposited by solutions subsequent to the forma- 

 tion of the limestones, and from the similar associations it seems 

 reasonable to connect their introduction with the suggested mode 

 of genesis of the tremolite. 



General characters. The fibrous talc is the predominant variety 

 and the usual grade consists of the same felted mass of fine fibers 

 that characterizes the tremolite schist. The fibrous nature is very 

 persistent and can be seen by the microscope to exist even in 

 samples that appear to the unaided eye as massive. Foliated talc, 

 that is the crystallized variety, occurs more specially in the mines on 

 the southwestern end of the belt. It is found as intercalated seams 

 between the fibrous talc. 



The fibrous variety is commonly known as agalite, whereas the 

 name rensselaerite is often applied to the foliated mineral. The 

 latter designation seems to rest upon a mistaken identification. The 

 type specimens of rensselaerite collected by Ebenezer Emmons show 

 it to be a mineral of the serpentine family, and to be an alteration 

 of pyroxene. 



The color of the talc is white or light gray, with a greenish tint 

 in the foliated variety. The freshly mined material bleaches to a 

 lighter shade on exposure to the air through the evaporation of the 

 mechanically held water. Near the surface the deposits show dis- 

 colorations from iron and organic matter, but at a depth usually of 

 40 or 50 feet they pass into commercial rock. 



There is no uniform practice followed in selecting or grading the 

 talc before it is sent to the mill. In most mines the foliated talc 

 forms such a small percentage of the average that it does not 

 influence appreciably the quality of the ground product. Certain 

 mines in the town of Fowler produced at one time considerable 



