A PRELIMINARY REPORT ON CLAYS OF rLORIDA 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 decor 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. Weathering 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 formerly believed that all clay resulted from the weathering of feldspathic rocks. Ries1 has pointed out that "there are some rock species, however, 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 insoluble 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 theclay 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.