Cretaceous Clays in Middle Georgia. — Ladd. 249 
and carved to a remarkable extent even v^'hen perfect- 
ly dry. It breaks with a conchoidal fracture and the 
joint planes are concentrically arranged. The joint 
planes are stained with iron oxide and the bed per- 
meated with veins of greenish colored sands 12 feet 
6. Green laminated clay, very plastic and containing black 
carbonaceous layers 8 feet 
A hand specimen shows a white to grayish clay with some- 
times a yellow to greenish tint, and having occasional stains 
of iron oxide along the joints. When dry, although exceed- 
ingly hard and tough, it cuts easily, and when cut it shows a 
smooth glossy surface which takes a good polish. In spite of 
its toughness it is porous, almost as light as cork, floating 
readily on water, although when placed in the water it slowly 
moistens, becomes pasty and, after a few minutes, sinks. Some 
scales of nuiscovite may be seen with the naked eve. The clav 
is not very plastic. 
Under the microscope there appears in this clay, a large 
amount of foreign materials, which consists largely of rounded 
grains of quartz, the largest being one-one hundredth of an 
inch in diameter. Occasional magnetite grains occur and also 
plates and prisms of muscovite and angular fragments of feld- 
spar. There are also a few small areas of a yellow colored 
mineral which seems to be titanite but which were not identi- 
fied with certainty. In addition to these impurities there oc- 
cur occasional fragments of an isotropic, colorless mineral, 
most likely basal sections of biotite. The clay particles are 
more or less bound together in little aggregates. 
Its specific gravity varies from 0.90 to 1.20, averaging near 
the former amount. Experiments with the dry powdered cla\- 
prove it to have an enormous absorptive power, the clav tak- 
ing up over two hundred per cent of its own weight of water. 
It shrinks on drying twenty-five per cent linear measurement. 
A dried l)ri(juette shows an average tensile strength of two 
hundred and thirteen pounds per square inch. 
On burning the dried clay shrinks an additional 6 per cent 
and burns from a buff to a pale yellow color, easilv crackling, 
and fusing at a temperature of 1330 degrees C. 
