64 FLORIDA GEOLOGICAL SURVEY-I5T1I 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 developed as a result of clay being one of the most abundant natural products. 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. Ries1 defines clay "as an earthy material occurring in nature whose prominent property is plasticity when wet." Merrill2 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. Orton3 says: "Strictly speaking, however, the term applies to a single mineral, viz., silicate of alumina or kaolinite." Wheeler4 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

 1Ries, H., Clays, Their Occurrence, Properties and Uses, p. 1, 1908.
 2Merrill, G. P., The Non-Metallic Minerals, p. 221, 1910.
 3Orton, E., The Clays of Ohio, Their Origin, Composition and Varieties. Ohio Geol. Survey, VII, Part I, p. 46, 1893.
 4Wheeler, H. A., Clay Deposits, Mo. Geol. Survey, XI, p. 17, 1896.