608 CLAY, MARLE, AND SAND. 



and extensive ; the former lying above the Pur- 

 beck limestone, and the latter immediately be- 

 neath the chalk. 



SYNOPSIS OF CLAY, MARLE, AND 

 SAND. 



CLAY. 



A. Ferruginous clay : scarcely ever plastic, red, 

 or yellow. Occurs in beds under trap rocks, and passes 

 into jasper ; where it is also noticed. 



B. Fuller's earth : dull green or grey : semi- 

 transparent, and crumbling, when in water. Occurs in 

 the upper sandstones, in the limestones, and in the red 

 marie sandstone. 



C. Schistose clay: white or grey: scarcely plastic 

 till after exposure to air, when it crumbles. Pipe clay. 

 Above the chalk in Dorsetshire. 



D. Indurated, generally in irregular nodules ; 

 very refractory in the fire. In the coal series. Stour- 

 bridge clay. 



E. Plastic clay, potter's clay, of various colours 

 and properties. Occurs in different parts of the 

 secondary series. It is perhaps not essentially dis- 

 tinct from C. 



F. Blue clay: London clay: plastic in various 

 degrees. Contains peculiar imbedded fossils, whence 



