1880.] NATURAL SCIENCES OF PHILADELPHIA. 253 



tube it exfoliates and gives off water. In optical characters 

 it is identical with common talc, having been found to have an 

 axial divergence of about 12°40', frequently distorted. . It is 

 marked with striations or cleavage planes crossing at angles of 60° 

 and 120°. In this respect it is like Jettei'isite or Culsageeite, 

 while in common talc such markings are rarely visible, and never 

 distinct. It has the chemical composition of talc, except that the 

 percentage of water is larger than usual, being 7-02 per centum. 

 None of this water is hygroscopic, as its weight remains constant 

 in a desiccator over sulphuric acid. 



The water of two other talcs from the same localit}^ was deter- 

 mined. A massive talc whicli does not exfoliate in the Bunsen 

 burner flame or in the platinum crucible, but does so at the point 

 of the blowpipe flame, contains 4.23 per centum of water. 



A foliated talc which is caused to exfoliate onlv very slightly 

 even in the blowpipe flame, contained 2.84 per centum of water, 

 and this was driven oS only at an extremel}'' high and long 

 continued heat. 



In these three talcs, therefore, we have the interesting results : 



1. That there is a direct ratio between the amount of combined 

 water and the amount of exfoliation. 



2. That there is a direct ratio between the tenacity with which 

 the water is held and the temperature at which exfoliation occurs. 



It is thought that perhaps these results may have a bearing in 

 an explanation of the propei'ties of the various Yermiculites. 



January 28, 1878. 



Tin in Nor^fh Carolina. — Mr. Lewis exhibited a small piece 

 of tin ore said to have been found in Surry Co., N. C, and which 

 had been handed to him for examination. It was a soft, light 

 earth}' mass of a brown color, crumbling when pres^^ed, which, 

 when held in a candle flame, became covered with small globules 

 of pure tin. The earthy base was a silicate of alumina, iron, and 

 lime, and was partially' soluble in acid. The tin was reduced b}^ 

 ver}^ gentle heat, for less than that required to reduce Cassiterite. 

 It was suggested that the tin existed in it either native or as an 

 ochre or hydrous oxide. No sulphides were present. It was 

 questioned whether the specimen exhibited was a genuine native 

 product. 



A New Locality for Gypxum. — Mr. Theo. D. Rand announced 

 his discovery of gypsum, as an eftlorescence upon gneiss, at a 

 quarry near Darby, Pa. 



