DEPARTMENT OF GEOLOGY 49 
The red-buming clays, which are red, pink, and yellow when 
burned. Chiefly used for brick, tile, coarse pottery, and other 
common uses. With these are placed the clays of similar prop- 
erties which burn to a greenish yellow from the presence of lime. 
The buff -burning clays, which burn to a buff color and 
include fire clays and most potters’ clays. 
The white and ivory-burning clays, which burn white or 
nearly so. Here are placed the kaolins, porcelain, and china 
clays, paper and pipe clays, and other comparatively valuable 
clays. 
A variety of useful minerals which resemble clays, either in 
composition, appearance or use, are grouped in a separate col- 
lection. Here are placed the ochres and other mineral paints 
which are chiefly colored clays. Fuller’s earths, used now 
chiefly for purifying fats and oils, talc, mineral soaps, and 
various other minerals of minor importance are included here. 
SANDS, SOILS, AND CEMENTS. 
The half of Hall 68 not occupied by clays contains the sands, 
soils, and cements. Numerous specimens of sand illustrate the 
varieties of sand adapted to different uses, such as molding sand 
for molds for metal castings; fire sand for infusible furnace 
hearths and furnace bricks; glass sand for the manufacture of 
glass, and sand for sand-lime brick, etc., and suggest some of the 
qualities a sand must possess to be adapted to any of these uses. 
Another series contains hydraulic limestones, cement rocks, com- 
mon limestones, clays, and marls suited to the manufacture of 
cement. All stages in the manufacture of Portland cement are 
illustrated. 
The composition, nature and varieties of soils are illustrated 
by a number of small groups showing: — 
The composition of soils ; 
The principal classes of soils; 
The plant foods which occur naturally in soils. (For foods 
added to soils, i. e., fertilizers, see Hall 78.) 
The formation of soil from an eruptive rock and from lime- 
stone is illustrated by two complete series showing the original 
rock and final product together with the intermediate products. 
A large number of soils from all parts of the world, arranged ac- 
cording to common classifications, illustrates the great variety 
of appearance and character which soils assume. Another series 
