64 FLORIDA GEOLOGICAL SURVEY—15 TH ANNUAL REPORT 
CHAPTER I 
GENERAL GEOLOGY OF CLAYS 
definition 
The general usage of the term clay is a very broad one and includes 
a large variety of substances. This liberal usage of the term has devel¬ 
oped as a result of clay being one of the most abundant natural prod¬ 
ucts. It is found in some form in practically every locality and is used 
for a great variety of purposes. No one definition of clay, therefore, 
can satisfactorily fulfill all requirements. This is partly due to the fact 
that the present knowledge of clays is far from complete, but more 
especially due to the fact that clays vary greatly in their properties and 
uses. No two clays are exactly alike. 
In any sense of the term clay is a substance occurring in nature 
which is plastic when wet, capable of being molded, preserves its shape 
upon being dried, and changes to a hard rock-like substance on being 
fired. Ries 1 defines clay “as an earthy material occurring in nature 
whose prominent property is plasticity when wet.” Merrill 2 describes 
clay “as a whole, as heterogeneous aggregates of hydrous aluminous 
silicates, free silica, and ever-varying quantities of free iron oxides and 
calcium magnesium carbonates, all in finely comminuted condition. 
Orton 3 says: “Strictly speaking, however, the term applies to a single 
mineral, viz., silicate of alumina or kaolinite.” Wheeler 4 says: “The 
scientific definition of the term clay is a more or less pure variety of 
the mineral kaolinite, the hydrous silicate of alumina.” He also gives the 
following as the popular definition of a clay: “Clay is an earthy material 
that becomes plastic when wet.” 
Thus it is seen that the principal definitions take two forms, viz., 
those based upon the property of plasticity and those based upon the 
mineral composition. Both of these are correct in that all clays are 
1 Ries, H., Clays, Their Occurrence, Properties and Uses, p. 1, 1908. 
2 Merrill, G. P., The Non-Metallic Minerals, p. 221, 1910. 
3 Orton, E., The Clays of Ohio, Their Origin, Composition and Varieties. Ohio 
Geol. Survey, VII, Part I, p. 46, 1893. 
4 Wheeler, H. A., Clay Deposits, Mo. Geol. Survey, XI, p. 17, 1896. 
