10 Geology and Mineralogy of a part of Massachusetts, &c. 
Vo designate the rock intended by an observer, it is neces- 
sary to resort to the several subdivisions. 
The hornblende rocks of this section are all primztave. 
They are 1. Hornblende and Hornblende slate, occurring 
as rocks, in which the hornblende is ‘ nearly or quite 
pure.”* 2. Primiiive Greenstone, or aggregate of horn- 
blende and feldspar, in which the ‘“‘ hornblende predomin- 
ates, and very frequently gives to this aggregate more or 
less of a greenish tinge, especially when moistened.”* ‘This 
mineral often bas a slaty structure, forming a variety, prum- 
itive greensione slate. “hese rocks are always associated 
with ‘‘ gneiss, mica-slate, or argillite.’* 3. Hornblende 
and Mica, the former in larger quantity and sometimes a 
little feldspar. It may be ealled micaceous priumative trap, 
or micaceous greenstone, with more propriety. 
The preceding rocks are abundant along the eastern part 
of the section, often associated, and always in beds in the mi- 
ca-slate. They are too abundant to need a specification of 
their localities, though I have not observed them to form 
very largebeds. Abouta mile east of the meeting house 
in Middlefield is a beautiful greenstone slate. Indeed that 
town, as well as the others in that line, contains all the above 
varieties of primitive trap. 
Associated with these rocks, is 
Sienite. 
This is an aggregate of hornblende and feldspar, in which 
the ‘feldspar is the most abundant ingredient, and the 
quantity of hornblende is sometimes small.”’* I have never 
observed this rock in great quantities. It is sometimes 
porphyritic. In Rees’ Cyc. itis stated that the feldspar of 
the real sienite is of a red color. In what is called Sie- 
* Cleaveland’s Min. and Geol. p. 743, 745, and 750. ‘The composition 
of these rocks, given in Rees’ Cyc. is the same as that quoted from this 
work. i 
+ On the high marshes, in the'town of Peru, which rest on this rock and 
mica-slate, is found the rare plant, Eriophorum cespitosum, Ph.; and in 
Stockb ridge in an elevated marsh at the foot.of a hill of mica-slate grows 
the Eriophorum alpinum, L. and Carer lenticularis, Mx. 
