37 
are very numerous, and they form the basis of many, impor¬ 
tant manufactures. Ochres of various colours, have been 
observed in several states. In these minerals, the clay is 
united with minute portions of iron, which gives them their 
various tinge of red, brown, and yellow.* * * § These shades 
may be varied by the application of heat. They are em¬ 
ployed for crayons, but are principally used as paints, in 
union with the dying oils, for the purpose of protecting ed¬ 
ifices from the effects of air and rain. Common clay is used 
in the manufacture of bricks,f and pipe clay , which is found 
in Vermont, receives its name from its use. Potter's clay 
is a common production $ and fuller's earth , a species so 
highly valued in Great Britain in the manufacture of wool¬ 
len cloth, that its exportation is forbidden by an act of parlia¬ 
ment, is said to have been discovered in South-Carolina.§ 
In addition to these, may be mentioned loam , a compound 
of great importance in soils, and felspar, which in its de¬ 
composed state, is used in the making of porcelain. From 
the analysis of Mr. Cloud, an officer in the United States 
mint, it appears that this mineral exists at Monkton in the 
stateofVermont.H It is this substance under the name of 
kaolin , or petunz.e , from which the Chinese porcelain is 
made. 
The several clays that I have noticed, are used in the mak- 
* The Terra lemnia found in the Island of Lemnos, is a red 
ochre. Brown ochre is often called umber , from a place in It¬ 
aly, where it is found, (Kidd.) The difference between boles and 
ochres, consist, in the latter containing most iron. 
f 25 million were made in one year in Msssachusetts (Morse.) 
% Clays are generally composed of silex, alumine, and oxyd of 
iron— Common brick clay contains considerable iron. Potters 
clay has generally some lime in its composition, which occasions 
it to vitrify on exposure to heat Pipe clay on analysis, resem¬ 
bles porcelain clay , but the siliceous particles are not sufficiently 
fine for the latter use. The clay of Limoges , from which French 
porcelain is made, consists of silex, alumine, and oxyd of iron. 
§ Fuller's earth contains a certain proportion of alumine, (not 
more or less than a fourth or a fifth of the whole mass) so as to 
render it diffusible through water. It is also necessary in order 
to answer its use, that the siliceous particles be very fine, else 
they would wear out the texture of the cloth to which they are 
applied, (Kidd’s Mineralogy, vol. 1, p. 176.) 
|| Med. Repos, vol. 14, p. 404. 
