ap) 
Se) 
TAB. CCXLVIL 
Coloured Clays. 
Oxxune of Iron seems mostly the colouring ingredient in 
Clays as well as in most other substances. The upper spe- 
cimen here figured is of a peculiarly delicate brown, with 
some greenish parts about it, and has a little of the frac- 
ture and appearance of Fuller’s Earth. It, however, is a 
very good Clay, readily plastic with water, which is suffi- 
cient to distinguish it from that substance. In this the 
green hue was stronger when first gathered. This came 
from the canal near the Kent road. It is not rare. 
The middle specimen came from a well in Richmond 
Park *, with colours as beautiful as any of Seps Marbles. 
The lilac tints may be ascribed to a portion of Manganese, 
the usual cause of crimson and purple tints. It may, how- 
ever, be owing to a mixture of two different Oxides of Iron, 
viz. the reddish, and the blueish or grayish. The lower 
one + displays also the bright Ochre red so mixed with the 
white and yellow, that we might almost call it Terra mira- 
culosa or Wonderful Earth, if that name were not already 
engaged by a Lithomarga found at Klanertz, of which we 
shall not fall far short when we exhibit the Lithomarga from 
Ireland. In the middle figure, the upper. surface is rather 
more polished than ordinary, and appears as if one mass 
had slipped over another. This is not uncommon in many 
fossils; for, when two substances pass over one another, 
they give each other a smoothness which is called Slicken- 
sides, as in Ores of Lead, &c. 
* 390 feet below the surface, 
+ 408 feet from the surface. 
