Argillaceous Oxide of Iron
This 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.