432 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
Milling. As above noted, the ocher milling practice at the various 
plants in the Cartersville district is fairly uniform. As mined the 
ocher contains a considerable quantity of coarse sands, with occa- 
sional fragments of quartzite. The presence of part of these impu- 
rities can be avoided by careful selection during mining, but owing 
to the manner in which the deposits have originated, the ocher will 
always contain some sand and quartzite, representing those portions 
of the original material which have not been entirely replaced. It is 
the object of the treatment described below to separate from the ocher 
as much as possible of these impurities. 
The ocher, brought in cars from the mines, is either dumped 
directly into a log washer or dumped on a platform and shoveled into 
the washer. The log washer consists of a log 12 to 20 feet in length 
and S to 14 inches in diameter. Iron teeth or paddles are set along 
the log in an irregular spiral. The log revolves in a trough (into 
which water flows) by power . applied to gearing at one end of an 
axis passing lengthwise through the log. The paddles, during the revo- 
lutions of the log, break up the material (crude ocher) fed in and 
gradually force the solid residue (sand, etc.) to the upper end of the 
trough, while at the same time the water carries off the lighter por- 
tion (containing the ocher and the finer particles of sand and clay) at 
the lower end of the washer. The ocherous water is led through a 
series of settling troughs 300 to 800 feet in length, set at a gentle 
slope. The heavier particles are deposited in these troughs, while the 
water, still carrying the fine ocher, passes on into large settling tanks. 
Here it is allowed to stand until the ocher has settled to the bottom. 
The overlying water, fairly clear, is then drained off through pipes 
set in the sides of the tanks. The ocher in the tanks is allowed to 
dry, under the ad ion of the sun, until it is solid enough to be handled. 
It is then shoveled out and taken to the drying house. The final 
drying takes place either on racks in the open air or over coils of 
steam pipe. The latter process is of course quicker, but results in 
the loss of part of the ocher, as that portion nearest the pipes is 
dehydrated too much and takes a reddish tint. After drying, the 
material is finely ground. The machine used for this purpose is a 
Clark pulverizer or other mill of the same type (disk pulverizer). 
