36 Geology of Massachusetts. 
tion : and were they as enduring as gneiss and granite, these latter 
rocks would soon be neglected. 
Tertiary Formations. 
I suspect there are only two varieties of these formations in Mas- 
sachusetts: one developed most perfectly in the west part of Mar- 
tha’s Vineyard, and the other, and the most extensive, along the Con- 
necticut river, although common in limited patches all over the State. 
Neither of these formations furnishes stones sufficiently firm for arch- 
itectural purposes, although in a few instances, I have observed lim- 
ited beds of the clay, sand and pebbles, that compose these forma- 
tions, to be ina state of consolidation. Nearly all our clays, howev- 
er, are in the tertiary formations, and these are so important in an 
economical point of view, as to demand a particular description. 
Porcelain Clay. 
This is the purest of all the clays, and is the only one employed in 
the manufacture of porcelain, or China ware. It results from the de- 
composition of granite; and hence we might expect to find it in 
Massachusetts ; since we abound so much in granite. As, however, - 
the manufacture of this ware has but recently been introduced into 
this country, little effort has been made to discover this clay. It 
has been announced, as existing in several towns in the State, al- 
though the bed in Savoy, described by Prof. Dewey, in his account 
of the geology of Berkshire, is probably the only one known that 
merits a notice in this report. It is said to constitute a layer three 
feet thick, and of unknown extent, several feet below the surface. It 
contains coarse particles of quartz, which can, however, be separated 
by sifting. It resembles the porcelain clay of Monkton, (Vt.) which 
is regarded as of a good quality. It forms a very cohesive white 
paste, and crucibles made from it, and burned in a common fire, 
were sonorous when struck. A similar clay is said to occur in large 
quantity, in Canaan, (Ct.) According to Dr. Porter, it is found 
likewise somewhat abundantly in Plainfield. 
A part of the extensive clay beds on Martha’s Vineyard, appears 
to be porcelain clay ; especially in Chilmark : though a large propor- 
tion of mica is mixed with it. 
Potter's Clay. 
_ This is the clay so extensively employed for common pottery, 
pipés, tiles, and bricks. And fortunately it is found on almost every 
