CLAY DEPOSITS. 657 ~ 
enough to vitrify, they are red, of various tints. There seems to bea 
difference in the mode in which the iron is in combination in the clays 
of the drift and in the fire clays of the State, the coloring due to the 
iron being not at allin proportion tothe amount. A fire clay containing 
3 per cent. of iron will be pale yellow in color, while a brick with 4 or 5 
per cent. will be a cherry-red. In the fire clay, however, the iron fre- 
quently shows in black spots, which would increase the average of the 
clay in iron without making any difference in its color, since it occurs 
in kernels and is not distributed. The clays of the drift are of very 
great value to us, as they are the source from which our building mate- 
rial is largely derived. They are better for that purpose than a purer 
clay would be, and their uniform plasticity makes their working easy. 
In another rising industry they figure prominently: that of making 
drain-tile. There is little or no distinction in the qualities of clay needed 
for these two uses. Good brick clays abound in every county covered 
by drift, though their qualities change in different parts of the State. The 
marks of the districts are not well defined, as the clays change too 
rapidly and too frequently to make much generalizing possible. Cincin- 
nati has a brick which is different from any found in other parts of 
the State. It has a dirty white color on its surface which is probably 
due to the water used in tempering, dissolving some soluble salts of the 
alkalies and earths present, and leaving them on the outside of the brick. 
When it is first heated in the kiln, as the fire deepens, the bodies flux the 
outside of the brick as described ; at any rate the outside of the brick | 
has not the even, regular, though light tint which the inside exhibits. 
Another trouble of drift clays is the occurrence of lime in small nug- 
gets which the process of manufacture does not remove; these are burned 
until caustic in the kiln, and then become hydrated when exposed to 
the air. They burst out, leaving holes in the brick, showing the white 
lime in the base of the cavity, and make'a very unsightly appearance. 
It is very seldom that a drift clay can be used for anything better than 
brick or tile, but some earthen-ware, such as flower pots, etc., are pro- 
duced from it. 
Occasionally, however, small patches of clay are found which are 
noticeable exceptions to this. An example is found at Springfield, 
Clarke county, where a bed of whitish clay, very similar to the Milwau- 
kee cream-colored clay, is found. It is a bed twenty feet thick, showing 
42 Gre 
