Varieties of Talcose Slate, 



353 



part, obviously members of the same formation, using this term too in 

 a very limited sense. 



Dr. Maceulloch describes talcose slate as differing from mica slate 

 only in the substitution of talc for mica : that is, it consists essentially 

 of quartz and talc. It is this variety that constitutes the principal 

 portion of talcose slate in Massachusetts. But other varieties are 

 found, as the following description will show. 



Mineralogical Characters. 



1. Schistose Talc. This variety is more or less distinctly foliated, 

 and varies in color from blackish green to very light green, or green- 

 ish white. (Nos. 789 to 793.) It is the least abundant of any of the 

 varieties. 



2. Steatite. This is obviously only a scaly and semi-granular or 

 partially indurated variety of talc. "We see," says Beudant, "by 

 these analyses, [which he had just quoted,! that the steatites differ 

 from talc only by the presence of water. These substances also occur 

 together and in precisely the same geological position. They appear 

 even to mix in all proportions, and in some suits of specimens, there 

 seems to be a passage from one substance to the other."* These re- 

 marks correspond exactly with the steatite of Massachusetts ; al- 

 though we have some beds of steatite which are associated with but 

 a small quantity of foliated talc. But in general, these beds consti- 

 tute a part of the talcose slate formation. 



The color of this variety is usually light gray. In some quarries 

 however, (as in Rowe and Zoar,) it is a delicate green ; and in such 

 cases the rock is obviously nothing but foliated talc, which is so com- 

 pact that it forms a fine stone for economical purposes. In the quar- 

 ries the green and the gray varieties alternate ; although there is no 

 seam between them ; and perfectly sound blocks may be obtained, 

 which are partly gray and partly green. (Nos. 794 to 805.) 



3. Chlorite Slate. Sometimes this variety is foliated and of a dark 

 green color ; and in such cases I know of no means of distinguish- 

 ing it from talc, except perhaps by its darker color. Generally it is 

 slaty in this region, and very minutely scaly. In this case it proba- 

 bly owes its slaty structure to a small proportion of quartz which it 

 contains. But the chlorite slate of the Hoosac mountain range is re- 



* Mineralogie, Tome ii, p. 212. 



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