40 GEOLOGY. 



The ease with which soapstone is wrought, the hand- 

 some polish it is capable of receiving, and its power of 

 resisting the effects of heat upon most other rocks, ren- 

 der it extensively useful in the arts. Besides its vari- 

 ous uses in connexion with heat, it is preferable to any 

 other material yet discovered for cylinders, used in 

 manufactories for dressing yarn to fit it for the loom. 

 The powder of this stone when mixed with oil, has 

 recently been applied to great advantage to the gudgeons 

 of wheels, axletrees of carriages, and to various other 

 purposes of a similar kind. 



Vermont and New Hampshire furnish soapstone in 

 great abundance, and of various qualities. A quarry 

 in Francestown, in the southern part of New Hamp- 

 ahire, has furnished more for Boston market and the 

 various manufactories in New England, than any other 

 deposit. Orford, New Hampshire, contains a beautiful 

 variety. Several towns in Vermont, near the Connecti- 

 cut river, contain it in great abundance, and of a good 

 quality. 



When a rock of a homogeneous base has crystals of 

 a certain character dispersed through the mass, it is 

 called poi'phyry. The base is more commonly some 

 variety of hornblende rock, but sometimes .<jlay-slate, 

 compact felspar, or graywacke. 



The crystals usually consist of felspar and quartz, 

 the former in prisms, the latter in pyramids, or small 

 nadules. 



The color of porphyry depends upon the base, and 

 the quantity of crystals dispersed through it. Some- 

 times the base is dark green, and even black, and the 

 imbedded crystals small. Other specimens are com- 

 posed of a lighter base and more numerous and larger 

 crystals. 



Some varieties of porphyry receive a beautiful polish, 

 when it furnishes a valuable material for tables, mantel- 

 pieces, and many smaller ornaments, such as butter 

 plates, snuff-boxes, kc. 



Vast deposits of this rock are found at Nahant, 

 Lynn, Maiden, Marblehead, Salem, Canton, and 

 several other places in the vicinity of Boston. In 



