290 GEOLOGICAL SURVEY 
posit of clay, 2 or 3 broad shallow tanks are arranged, so that the water from one may flow into the next. 
Above the first, a short inclined plane is placed, and a trench leads from it to the tanks, which are 
called catch-pits. A portion of the clay is placed on the plane, and a stream of water conducted to the 
spot, is made to fall on it, which washes it down to the trench and into the tank, where the quartz 
grains subside, the finer particles being carried forward to the next pit. The clay, however, is not al- 
lowed to rest, till it reaches the last pit, when it has parted with all the quartz. ‘The water, when 
clear, is drawn off, at plug-holes. When the tank, by repetition of this process, becomes filled, all 
the water is drawn off, and when the clay is so dry as to be cut into cubic blocks, it is taken out and 
dryed in sheds, and is then ready for the market. 
When the clay is free from sand and impurities, all that is necessary, is to excavate and dry it. 
Of the artificial variety, seven or eight thousand tons are exported annually, from these works. It 
appears thai from the south-west of England, materials used in the potteries are exported annually, 
to the value ,of $250,000. 
The process that I have described is simple and not expensive. 'The decomposing grits of Platte’s 
Springs could be washed in this way, if better sources of the clay did not occur. 
Fire bricks are sold in Boston at from $5 to $6 per hundred. Would it not be worth while to at- 
tempt the manufacture here? 
For glazing pottery, there’are abundant materials in the felspar of the coarse granites, and even 
in the eurite of the slate. 
The bed of silicious clay of the buhrstone, will furnish a material of value in the manufacture of 
pottery. 
Mareriats For MILusTrones. 
The beds of silicified shells, of Barnwell, will furnish an excellent material for this purpose. Pieces 
may be found that agree exactly with the French buhrstone, but those who have attempted to pro- 
cure millstones at this locality, have committed a great mistake in trying to get them in one piece, 
Every one knows that French burr mill stones are made up of from 16 to 20 pieces, cemented and 
bound together with iron hoops. 
By properly selecting the pieces, very excellent millstones may be procured at this place. The 
principal locality oceurs on Cedar creek, within a few miles of the rail road. 
There is above Dean Swamp, Orangeburg, a bed of close grained silicious rock, also belonging to 
this formation, which is explored for millstones, but nearly all those that are not imported are pro- 
cured from the coarse granites. 
MATERIALS FoR PAInts. 
A very fine yellow ochre of a rich color and fine quality is found in a deep ravine at Lang Syne, 
in Orangeburg. I showed this to several artists, who pronounced it equal, if not superior, to the best 
English or French ochres. Red and yellow ochres are abundant in Chesterfield, and localities are 
known throughout the lower beds of the Eocene. The Orangeburg ochre needs no preparation, but 
ochres, in general, require to be separated from the sand with which they are mixed. For this pur- 
pose the best process is that I described for the preparatian of China clay. 
Soapstone is often ground with whale oil, as a paint for common purposes, and especially for the 
roofs of houses, it is said to answer well. The fine soapstone associated with the magnetic ores, 
and that at Brewer’s mine, furnish all that can be desired for this purpose. 
