2 W. H. Brewer—Suspension and Sedimentation of Clays. 
The transportation and deposition of gravels and coarse 
sands are probably in accordance with well-known hydraulic 
and the relative weight and surface of the transported materials 
are the only factors that need be considered in any practical 
set Caan But with those finer particles of disintegrated 
s which are ultra-microscopic in size and all those which 
ironeh still coarser are small enough to be subject to those 
movements in liquids known as the “ Brownian motions,” and 
with the true clays I consider that chemical conditions rather 
than mere motion of the water are the controlling factors. 
I have carried on a long series of experiments on the sedi- 
. Sega of clays, and the finer portions of soils and pulver- 
d 
to light, temperature, etc. 
There is considerable difference as to details in the behavior 
of various clays in water. With some of them, if agitated and 
thoroughly diffused through the liquid and then allowed to 
stand at rest, the turbidity fades gradually and regularly in 
Seusliy from the pots to the top, and the liquid gradually 
grows clearer until it becomes as clear as natural waters ever 
. sually however, and with the great majority of clays (if 
the water be pure enough), the deposition is in quite a differ- 
ent manner. After some time, it may be in a few hours or it 
may be only after some days, the suspended material disposes 
itself in layers or strata which are more or less obvious because 
of the different degrees of turbidity of the liquid. There may 
be but two or three of these layers to be seen at once or there 
may be six or eight, the number depending in pars on the com- 
position and fineness of the material under experiment, in part 
on the freedom of the water from other Senter material than 
the clay itself, and in part on the temperature. Some of these 
layers may be and usually are very obvious, others obscure and 
only to be seen in the best light; some are very sharply de- 
fined, others remain ragged and ill defined along the line of 
separation. me which may be obscure at one temperature 
become sharp and well-defined if the temperature be slow 
raised or lowered a few degrees, or well-defined strata at one 
temperature become first hazy and then disappear at a higher 
or lower temperature. Sometimes, with a change of tempera- 
ture, what was before one uniform stratum will slowly resolve 
itself into several obvious strata, which remain distinct so long 
