14 Geology of Massachusetts. 
tance. Those that are employed for architectural or ornamental 
purposes, first claim attention; because the state is peculiarly rich 
in treasures of this kind. It will be easy to see, by a reference to 
the Map, how extensive are the formations: from which they are de- 
rived ; although it must not be concluded that every part of a forma- 
tion will furnish materials of equal value for economical purposes. 
Grantie and Sienite. 
Much confusion has arisen in the application of these terms. 
They were originally applied to designate rocks very different, if not 
in composition, yet in their geological relations. But most of the rock 
that is generally described as sienite, is a variety of granite. This is 
certainly the case in Massachusetts. Wherever the granite admits 
hornblende into its composition, I have considered it as sienite ; and 
not unfrequently the hornblende constitutes the principal ingredient ; 
taking the place, more or less, of the quartz and mica, so as to form 
a compound of hornblende and feldspar. This compound forms 
some of the most beautiful varieties of sienite, though extremely 
hard to work for architectural purposes. But not a little granite that 
contains no hornblende goes by the name of sienite. Thus, much 
of the Quincy granite is wanting in hornblende; but being almost 
destitute of mica, and having the close aspect of sienite, it is called 
indifferently by either name. 
The variety in the composition, color and hardness of these rocks 
in Massachusetts, is almost endless. The quartz and feldspar are 
commonly white, yellowish and gray; the latter not unfrequently 
flesh colored: the mica is very often black, but sometimes of a 
silver color. When the quartz prevails, the rock is easily broken, 
but hornblende renders it tough. The predominance of feldspar 
generally gives the rock a more lively white color and renders it 
rather easier to work. But I shall not attempt to describe particu- 
larly all the varieties of these rocks that occur in the State. Ani 
merous other varieties which I have met with in different localities. - 
The very coarse varieties of granite, which are found in some parts 
of the State, do by no means furnish a good building stone : indeed, 
some of theni hardly serve for common walls. Much of the granite 
in the Vicinity of the Connecticut river is of this description ; as also 
a considerable portion of the range which extends from Southboro’ 
