11 



TAB. CVII. 



FERRUM argillaceum. 

 Argillaceous Oxide of Iron. 



1 his is nearly the same as that figured in the last plate ; 

 but it has pebbles and gravel about it, which are cemented 

 with it into a hollow box-like form. It was discovered by 

 an endeavour to break the stone from off the top of the 

 upper figure, and thus formed a lid to the box. This was 

 given me by T. Marsham, Esq. F. L. S. The lower figure 

 is curiously concentrated with light ochre and a darker 

 umber, and serves to give an idea of the formation of some 

 pebbles, particularly of the nature of those called Egyptian 

 pebbles, (not the most admired sort,) of which more will 

 be said hereafter. 



