110 
It would appear, by the experience of Klaproth, that the 
blue Iron Ores, commonly so called, are the effects of 
Phosphorus; although Mr. Kirwan doubted it, as I have 
observed at fab. 10. The darker. blue Iron Ore, called 
Native Prussian Blue, from North Wales, which I had 
with Mr. Day’s collection, and also by favour of a friend, 
from near Aberdeen, are more solid, and darker, than that 
figured, and will serve to fill up the arrangement. I believe 
them to be nearly the same as to the colouring ingredients 5 
this being more mixed with a darkish Clay, which gives it 
the appearance of Indigo Blue. Thus we see the three 
primitive tints may be found in Ochres, and more or less 
in the Clays, as some of the Welsh specimens have rather 
more Clay than others, although not worth a different spe- 
cification ; and the whole serves an important purpose, viz. 
to satisfy us pretty nearly as to what may be expected from 
coloured Clays, or Ochres, as I show the brightest I have 
seen of them. 
That they may be mixed to form greens may sometimes 
happen in nature; but T have only seen it so in Clay, as 
mentioned and figured tal. 247. Greens scem more com- 
bined in another way, as with Chlorite, Terre-vert, or Talc, 
as. tab. 182, lower fig., and among the precious stones the 
Emerald is green, which is said to be caused by Oxide of 
Chrome. 
Colours are only brilliant by means of the substance 
which reflects them, as I shall show in my New Arrange- 
ment of Colours. 
Brown Earths are called Umbers; but are very much 
allied in their nature to the Ochres. Thus they may, with 
some regularity, be placed near them in this instance. 
Common Umber of the shops is of this kind, and will 
burn darker; hence we have raw and burnt Umber. 
Clayey Iron Stones often approach the appearance of the 
Umber used by painters, of which the best is said to 
