91 
TAB. CCXLVI. 
Brown Clay. 
Bricks, tiles, pans, and garden pots are most commonly 
made of these brown Clays, which do not differ much in 
quality. The lighter brown Clays generally make the 
lightest-coloured bricks, their texture chiefly depending on 
the sand. The common brown Clays are preferred for 
modelling at the Royal Academy, &c. The upper figure 
represents a specimen of good red brick Clay, which was 
found 85 feet below the surface of the ground in Richmond 
Park. Sometimes the beds of Clay lic more in strata than 
at others, and when out of their places separate in a slaty 
manner. A specimen found at 138 feet of depth at the 
same place, is something in this manner—see the middle 
gure—which is rather grayer-coloured and more sandy, 
and is generally called Blue Clay ; taking its name from 
the blue cast it has when fresh dug. This probably pro- 
ceeds from the blue or gray Oxide of Iron, which soon 
bleaches. I have seen it where there have been rifts, allow- 
ing passage for water, when, in the parts where the light 
did not enter, it has shown the most vivid Prussian blue and 
purplish tints; but these on exposure to light passed off in a 
few minutes. All wet substances are darker than dry ones; 
but in these it is most remarkable—see the darker blotches 
on the left hand of the figures. 
