CHAPTER I. 



CLAY AND ITS MODE OF OCCURRENCE 



CONTENTS. 



Definition. 

 Origin of clay. 

 Residual clay. 



Form of residual deposit. 

 Depth of residual deposit. 

 Sedimentary clay. 

 Marine clays. 

 Estuarine clays. 

 Swamp and lake clays. 

 Flood plain or terrace clays. 

 Drift or bowlder clays. 

 Secondary changes in clay deposits. 

 Mechanical changes. 



Tilting, Folding, Faulting. 

 Erosion. 

 Chemical changes. 

 Change of color. 

 Leaching. 

 Softening. 

 Consolidation. 

 Concretions. 

 Shale formation. 



Definition. — Clay is the term applied to those earthy materials 

 occurring in nature, whose most prominent property is that of 

 plasticity when wet. On this account they can be molded into 

 almost any desired shape, which is retained when dry. Further- 

 more, if heated to redness, or higher, the material becomes hard 

 and rock-like. Physically, clay is made up of a number of small 

 mineral particles, ranging from grains of coarse sand to those 

 which are of microscopic size, or under one one-thousandth of 

 an inch in diameter. (Figs. 30-34.) Mineralogically, it con- 

 sists of many different mineral fragments, some of them fresh,. 



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