M. Godon’s mineralogical observations. 137 
that it admits occasionally, and sometimes in its whole mass, the sey- 
eral minerals mentioned among the species of amphiboloid. 
The general aspect of this rock approaches it to the granite, from 
which it differs sometimes only by its geognostic situation. It pre- 
dominates north of Boston, and on the south side of that place (about 
nine miles), where it forms an extensive ridge, which appears to be 
spread from the east to the west, beginning from the sea coast. 
14. Felsparoid is often formed of nothing but felspar and amphi- 
bole. It then occurs principally north of Boston. _ The felspar in it 
is sometimes red-brown, but more frequently whitish, with an imper- 
fect lamellary texture, and an aspect somewhat greasy [Chelsea o]. 
Sometimes white and red felspar are united in the same specimen. 
To this kind I give the name of common felsparoid. 
15. This rock is more frequently found consisting of uncoloured 
felspar, hyaline quartz, amphibole, and sometinies small particles of 
tale of a light green colour. _Felspar, which forms the greatest pro- 
portion, is frequently whitish, but often with a light brown or reddish 
brown’colour. Quartz is the next in proportion; and amphibole, of 
a dark blue, or an imperfect black colour, exists sometimes, but in 
rare crystals, disseminated through the other elements. This amphi- 
bole is sometimes attracted by the magnet. Such is the composition 
of the rock, which exists in vast body at Weymouth, Braintree, and 
Quincy, (9) from whence it is transported to Boston for the purposes 
of civil constructions, particularly for making the first courses of buil- 
dings. There is a variety consisting of crystals of amphibole of a 
bright black colour, disseminated through white felspar of a pearly 
aspect. It is susceptible of a good polish, and is found beautiful on 
the north side of Boston [Newburyport turnpike o J. = 
‘I consider also as of aie species a variety of a Pleas eich, 
somet; 1 = ly, not in large masses, but 
abn hUny VULeuts wv ee] 
pe: 
