DEPARTMENT OE GEOLOGY 
45 
A variety of useful minerals which resemble clays, either in 
composition, appearance or use, are grouped in a separate col- 
lection. Fuller’s earths, now used chiefly for purifying fats 
and oils, talc, mineral soaps and various other minerals of minor 
importance are included. 
A collection of mineral paints comprises examples of those 
mineral substances which are used as pigments after some very 
simple treatment, such as grinding, washing or gentle calcining. 
The larger number of these as displayed are: (1) the earths and 
the ochres, which are clays colored with oxides of iron or bitum- 
inous materials, and (2) the metallic paints, which are iron ores 
ground or roasted. 
That part of Hall 68 not occupied by clays contains the sands, 
soils and cements. Numerous specimens of sand illustrate the 
varieties adapted to different uses, such as molding sands for 
metal casting; fire sands for infusible furnace hearths and fur- 
nace bricks ; glass sands for the manufacture of glass, sand 
for sand-lime brick, etc. These suggest some of the qualities a 
sand must possess to be adapted to any particular use. Another 
series contains hydraulic limestones, cement rocks, common 
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 
according to common classifications, illustrate the great variety 
of appearance and character which soils assume. Another series 
is arranged according to the more elaborate classification of the 
U. S. Department of Agriculture. 
