132 M. Godon’s mineralogical observations. 
The proportion of clay, which forms a part, often considerable, of 
all the alluvial ground, on which rest almost all the buildings of the 
town of Boston, is a happy circumstance, which prevents the infiltra- 
tion of sea-water, and which thus permits our obtaining, at a very 
short diStance from the harbour, and even from under the sea itself, 
fresh and sweet water. 
3. The waters, which flow under the ground, or which issue in 
springs at its surface, are frequently impregnated with foreign princi- 
ples. ‘These are principally carbonic acid, carbonated lime and iron, 
sulphated magnesia, and sometimes muriated lime and magnesia. 
Amphiboloid. 
_ 4. In a western direction from Boston, the rock, which occurs: 
first, is amphiboloid,. which passes frequently to felsparoid, and some- 
times so abruptly, that it is very easy to get them both unifed in the 
same specimen. These two rocks, which always alternate, appear 
predominant in the northern as well as western part of Massachusetts. 
They appear in some islands of the harbour [outward Brewster], and 
are directed, even under the enclosure of the town of Boston, where 
they break through the mossy ground of the common.. 
5. Amphiboloid is very variable in its aspect, and in the proportion 
and disposition of its constituent principles. Amphibole, which is. 
considered as its base, is commonly dark-greenish, grey, or black, of — 
great intensity, frequently with a lamellated texture. The rock appears 
sometimes consisting of, this substance alone, of an uniform colour,. 
or intermixed with light spots or veins of white and rosy felspaty. 
and magnetic sulphurated iron [Waltham]. I then call it common: 
amphiboloid. 
The two elements are frequently fitted together in such a mannef,- 
as to present irregular black and white spots. The felspar is com- 
