Geology of Massachusetts. 41 
real buhrstone, may admit of doubt; since it is unquestionably a rock 
of primitive formation ; whereas the real Paris buhrstone, is a mem- 
ber of thetertiary formation. But in an economical point of view, 
this question is of little importance, since the rock seems to answer 
nearly all the purposes of buhrstone so well that it is employed 
somewhat extensively for millstones. ‘These are manufactured near 
the ledge, and sold for seventy or eighty dollars each. I am told 
that they answer well, especially for the coarser kinds of grain. I 
should presume that the only difficulty would lie in their being less 
tough than the genuine buhrstone. ‘The quantity at the ledge is 
inexhaustible. 
Sometimes our citizens employ the finer and more compact va- 
rieties of granite for millstones. I have seen even a coarse conglom- 
erate, or puddingstone, used for this purpose. And while upon 
this subject, I cannot but express my surprise that no attempt has 
been made to employ our greenstone, and other hornblend rocks, for 
millstones. In Great Britain, basalt has been, within a few years, 
used for this purpose, and found even superior to the French buhr- 
stone; and our greenstone is only a variety of the same rock: in- 
deed, some of our greenstone cannot be distinguished, by the eye, 
from the European basalt. It is generally extremely compact and 
tough; and although its preparation might require a little more labor 
than the buhrstone, yet it would doubtless last enough longer, amply 
to pay for the additional labor. In the vicinity of Boston and along 
the Connecticut river, as may be seen on the Map, greenstone ex- 
ists in great quantities. It also occurs in small beds throughout the 
whole extent of the gneiss region ; and of a kind, which I should 
suppose from its appearance, would answer the purpose even better 
than that of the extensive ranges above mentioned. 
Coal. 
Of this mineral, the object of so much interest in every civilized 
country, there are found three distinct species; all of which are 
sometimes employed as fuel. The most common in Europe, which 
is there considered the best, is the bituminous coal, or that contain- 
ing bitumen. This burns readily with a yellow or white fame. A 
second species is the anthracite, or stone coal; which is generally 
described as burning without flame, because destitute of bitumen. . 
The anthracites of this country, however, burn with the flame that 
results from the combustion of hydrogen; this gas existing in a state 
Vou. XXU.—No 1. 6 
