A PRELIMINARY REPORT ON CLAYS OE ELORIDA 
65 
plastic to a greater or less degree and probably all contain some form 
of hydrous aluminum silicate, in widely varying quantities.* 
ORIGIN 
A clay is in all cases a secondary product resulting from the decom . 
position and disintegration of pre-existing rock. If the clay remains 
in the space formerly occupied by the parent rock it is said to be residual. 
If, however, the clay is transported, either by wind or water, and then 
deposited it is termed a transported or sedimentary clay. 
The breaking down of one rock and the resultant formation of clay 
is one of the processes of rock weathering. This includes both chemical 
action (decomposition) and mechanical action (disintegration) which 
are often carried on at the same time and are very closely related. Weath¬ 
ering takes place chiefly through such atmospheric agencies as rain, 
frost, wind, changes in temperature, through organic agencies as plants 
and animals, and through the action of atmospheric gases. 
Igneous rocks are the primary sources of all other rocks and are 
then the original sources of all clays. Limestone or shale residual clays 
are only indirectly derived from igneous rocks and have previously 
gone through one or more processes of weathering and sedimentation. 
Rocks containing feldspar may weather into clay. In fact, it was for¬ 
merly believed that all clay resulted from the weathering of feldspathic 
rocks. Ries 1 has pointed out that “there are some rock species, how¬ 
ever, that contain no feldspar (such as serpentine), and others with very 
little (as some gabbros), which, on weathering, produce some of the 
most plastic clays known.” In the process of weathering the more in¬ 
soluble portions, such as some of the aluminum silicates, accumulate 
and the more soluble constituents, as lime, magnesia, potash, soda, and 
sometimes silica, are carried away. 
During the weathering process the clay which consists of very fine 
particles may be left intimately mixed with larger particles of sand and 
other material. If this mixture is carried away by the action of running 
water a separation of the clay from the coarser material may result. Such 
a separation has often been the cause of the formation of large bodies 
*Soil investigators have still other definitions for clay based on fineness of grain 
rather than plasticity or chemical composition, one being all soil particles less than 
.005 mm. in diameter, and another that part of the soil which will remain suspended 
in an 8-inch column of water for 24 hours. Slightly coarser and non-plastic material 
is distinguished as silt. (See Hilgard, Soils, pp. 57-62, 83-85, 1906.) H. G. 
