Potter's Clay. 37 



decomposition 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, although 

 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 sift- 

 ing. It resembles the porcelain clay of Monkton, (Vt.) which is re- 

 garded as of a good quality. It forms a very cohesive white paste, 

 and crucibles made from it, and burned in a common fire, were sono- 

 rous when struck. A similar clay is said to occur in large quantity, 

 in Canaan, Ct. 



A part of the extensive clay beds on Martha's Vineyard, appears 

 to be porcelain clay ; especially in Chilmark : though a large pro- 

 portion of mica is mixed with it. 



Potter's Clay. 



This is the clay so extensively employed for common pottery, 

 pipes, tiles, and bricks. And fortunately it is found on almost every 

 square mile in the State. We have two quite distinct varieties. The 

 purest, sometimes called pipe clay, is found almost exclusively on 

 Martha's Vineyard. This is white, and contains usually so little 

 iron, that when burnt, it becomes still whiter, and will resist a high 

 degree of heat. Hence it is employed for making what are called 

 fire bricks, which are used for lining furnaces. White pottery is also 

 made from it. But the more common clay turns red on burning, in 

 consequence of the oxide of iron in it ; and this renders it much ea- 

 sier to be melted by the heat, and consequently diminishes its value. 

 It is of immense value, however, to the State ; because good bricks 

 may be made from it ; and because it exists so abundantly in almost 

 every town. The same tertiary formation that supplies clay so plen- 

 tifully, yields an abundance of sand for the mortar by which they 

 must be cemented. This sand, however, is generally rather fine ; 

 and I am inclined to believe, from all that I can learn, that our mor- 

 tar is generally prepared from sand that is too fine. 



