316 REPORT OF NATIONAL MUSEUM, 1899. 



Composition. The varying composition of talc is shown in the series 

 of analyses given below. 



Analyses of talc. 



FeO. 



MgO. 



Totals. 



Not 

 deter- 

 min- 

 ed. 



100.00 

 100.00 



The following analyses of soapstone have been made in the labora- 

 tory of the department: 



Analyses of soapstone. 



Occurrence and origin. Talc in all its forms is presumably always 

 a secondary mineral, a product of alteration of other magnesian 

 silicates. 



Smyth has shown * that the talc beds of St. Lawrence County, New 

 York (Specimen No. 63173), are alteration products from schistose 

 aggregates of enstatite or tremolite, principally the former. Accord- 

 ing to this author, the talc occurs, not as has been stated, in the form 

 of a well-defined vein with walls of granite or gneiss, but in the beds 

 lying wholly within the schistose portions of the prevailing limestone. 



The following account of these deposits as occurring near Gouv- 

 erneur is by A. Sahlin : 2 



The village of Gouverneur is situated near the northwest edge of a 

 geological island of Azoic rocks; granite, gneiss, limestone, and marble 



School of Mining and Forestry, XVII, No. 4, 1896. Also Fifteenth Annual 

 Report of the State Geologist of New York, 1895, pp. 665-671. 

 2 Mining and Scientific Press, May 11, 1893. 



