A GEOLOGICAL HISTORY. 59 



which lime is used in building and for agricultural 

 purposes. 



5th Brick Clay. — (See plate 5, fig. 5.) This is 

 a diluvium clay, of two varieties of colour, the 

 top is a light buff or dun colour, while the bottom 

 is of a light slate blue, containing some black 

 vegetable matter ; large quantities of brick are 

 made from a mixture of the two varieties of this 

 clay : on the top of this clay, is a diluvium of gravel 

 and sand, which is also used in the composition of 

 the brick. This bed of clay is from eighty to one 

 hundred feet thick. 



