36 fiF.OLOGV. 



in the same vicinity, are deposits of this useful and 

 beautiful rock, in sufficient quantities for building a 

 thousand cities of the size of Boston. 



In these deposits, the sienite uniformly consists of 

 three ingredients, though in others, it is formed of two, 

 the quartz being wanting. The three ingredients in 

 this useful material, will be readily seen by a glance at 

 the front of the Tremont House, where three colors are 

 distinctly visible at the distance of several rods. The 

 red and most abundant ingredient is felspar; the white, 

 quartz; and the black and least abundant is hornblende. 

 They are equally distinct in numerous other buildings 

 in almost every part of the city of Boston. 



Greenstone, or trap rock, is composed of hornblende 

 and felspar. The former always predominates, and 

 commonly constitutes almost the whole mass. 



This rock contains a large portion of iron, and is 

 hence heavy, hard, and more difficult to break than any 

 other stratum. It is, however, intersected by numerous 

 scams, by which it is separated into convenient masses 

 for erecting the walls of houses, for which it is exten- 

 sively used in New Haven, Edinburgh, and many other 

 places, where it is found in abundance. 



Two extensive ranges of mountains in New England, 

 commence with the East and West Rocks, about two 

 miles from the city of New Haven, both of which are 

 greenstone. One continues in the eastern range as far 

 as Greenfield, a part of which are Mount Holyoke and 

 Mount Tom. The other range passes farther west, and 

 extends to the Green Mountains in Vermont. 



The Giant's Causeway is a hornblende rock, called 

 basalt. 



Sandstone js associated with greenstone, and is always 

 placed beneath it, when they occur together. 



This rock, as its name denotes, is composed of sand, 

 or grains of quartz and felspar, with fine scales of mica 

 sometimes dispersed through the mass, and cemented 

 with clay and the oxide of iron. 



Many thousand tons of this rock have been car- 

 ried to Boston from Chatham, opposite to Middletown, 

 on the Connecticut river, and more or less is transported 



