48 



Economical Geology. 



erable depth ; and probably the exploration may be profitably con- 

 tinued for a long time with little machinery. 



Graphite is employed for pencils, crucibles, lubricating machinery, 

 &c. It occurs at several other localities in Massachusetts, besides that 

 in Sturbridge, but not in large quantities, except perhaps in Hinsdale. 

 It is said that a good bed of it has been opened in New Hampshire. 



A substitute for Emery. 



No real emery has yet been found in Massachusetts ; but a rock 

 composed of garnet and anthophyllite or augite, occurs in North 

 Brookfield, which is employed as a substitute for that mineral, and 

 it is said to answer well. The powder of the garnet, although much 

 inferior in hardness to real emery, is indeed sometimes called in com- 

 merce, red emery. The rock in Brookfield is abundant, and may 

 prove valuable. 



Tripoli or Rotten Stone. 



At Paine's quarry of limestone in West Springfield, I found a min- 

 eral which subsequent examination has convinced me is genuine rot- 

 ten stone: and so far as I have had opportunity of examining it, it 

 appears to be of a superior quality. I did not observe whether it can 

 be obtained in large quantity, though I saw not a little of it. Should 

 it prove to be abundant and genuine, it would be a valuable addition 

 to our economical minerals. 



A similar mineral occurs in the new red sandstone at South Had- 

 ley Canal. But I do not yet know its extent or precise situation. 



Native Alum. 



This valuable substance has recently been found in at least two pla- 

 ces in Worcester county. It occurs on a variety of the gneiss rock of 

 that county in delicate plumose or feather form masses along with 

 copperas. Both these substances undoubtedly proceed from the de- 

 composition of the rock and the iron pyrites which it contains. Hence 

 as we know that artificial means will aid the production of copperas 

 we have reason to suppose that it will do the same in respect to the 

 alum as we know is done in other rocks. But no trial that I know of 

 has yet been made. I have received this alum from two places viz. 

 Leominster and Barre. A fuller account of it will be given in the 

 third part of the report. 



