SECOND ANNUAL REPORT—PULLERS EARTH. 259 
(U. S. Geol. Surv. Bull. 315, p. 282, 1907) : “Fullers earth has for its 
base a series of hydrous aluminum silicates. These silicates differ in 
chemical composition, but are similar in that they all possess an amor¬ 
phous colloidal structure. These colloidal silicates possess the power 
of absorbing and retaining organic coloring matter, thus bleaching oils 
and fats.” 
UsesThe Florida fullers earth finds its chief use in filtering 
mineral lubricating oils. According to Day, “The common practice 
with these mineral oils is to dry the earth carefully, after it has been 
ground to 60 mesh, and run it into long cylinders, through which the 
crude black mineral oils are allowed to percolate very slowly. As a 
result the oil which comes out first is perfectly water-white in color, 
and markedly thinner than that which follows. The oil is allowed to 
continue percolating through the fullers earth until the color reaches 
a certain maximum shade, when the process is stopped, to be con¬ 
tinued with a new portion of earth. The oil is recovered from the 
spent earth.” 1 It is also used to some extent for lightening the color 
of cotton seed oil, and lard oil, although the English fullers earth is 
better, for these purposes. The original use of fullers earth, that of 
cleaning, is now one of the minor uses. It is said to be used in the 
manufacture of some soaps. It is used in cleaning furs and by drug¬ 
gists as an absorbent. 
Methods of Mining:—Originally the overburden in the Florida 
fullers earth mines was removed by pick and shovel. At the present 
time, however, the overburden is removed chiefly by steam power. 
The depth of overburden that can be profitably removed is determined 
entirely by the depth and character of the fullers earth deposit. The 
overburden removed in the mines which are now being worked varies 
from one or two, to twelve or fourteen feet. The greater part of this 
overburden is more or less decayed and residual in character and is 
readily removed. With some of the harder material, loosening l )y 
blasting becomes necessary. It is of interest to note that the fullers 
earth when protected by a great thickness of overburden sometimes 
contains irregularly distributed and residual masses of an impure 
clayey limestone. This was noticed in particular in the fullers earth 
mines at Quincy. At this place it was found that when in working 
back into the hill the overburden reached a thickness of twelve to 
fourteen feet, the fullers earth stratum contains irregular residual 
masses becoming more and more abundant until with an overburden 
of about fourteen feet the pit was abandoned. 
The fullers earth itself is mined in the open pit by pick and shovel, 
being loosened when necessary by blasting. From the pit it is loaded 
1 U. S. Geol. Sur. 21st Ann. Rept. pt. vi, (cont.) p. 592, 1901. 
