282 TJie Amciican Geologist. Novetaber, i89» 
mineral units of our rocks, and which affect these latter so 
considerably in the details of their composition and texture, 
are also directly in part dependent upon this strain on the sur- 
face of water. 
Floccidation. 
The phenomena of flocculation have been discussed by 
various authors, largely in connection with the subsidence of 
small particles in li(|uids. Among these are Hilgard, lirewer. 
Ijarus, Whitney, Hunt, Skey, Rawley and Bliss. 
The first three named considered the flocculation of such 
particles and their behavior on the addition of certain solu- 
tions as due mainly to chemical action, such as hydration and 
dehydration. Prof. Wliitney, however, and subsequent writ- 
ers have urged a physical explanation, claiming that the fine 
particles rendering water turbid are precipitated through floc- 
culation, which results from the altered "potential" of the sur- 
face particles of the water, due to the addition of certain salts 
to the liquid. 
If the particles in suspension attract the water more than 
enough to overcome its surface tension, molecules of water 
will tend to crowd toward the substance, and such particles 
will be forced from each other and continue in suspension. 
But if, on the other hand, these conditions are reversed, the 
tendency to contract exposed surfaces will operate, wherever 
possible, to unite particles, since this diminishes the amount of 
such surface. This process increasing the weight of the ag- 
gregations relatively much faster than the amount of surface 
exposed, where friction tends to prevent subsidence, allows 
them to settle, and leave the liquid clear. 
In this manner we account for the sudden subsidence of 
small particles suspended in rivers, where these enter the salt 
waters of the sea, which are of still higher specific gravity; 
and this process must be looked upon as of geological interest 
if not importance. 
Of more significance is the effect of such flocculation upon 
the texture of our soils, which is shown to be so largely mod- 
ified by the presence or absence of substances in solution that 
the production of crops, and the power of the soil to support 
plant life, may be profoundly affected by the use of such so- 
lutions, without reference to their fertilizing powers. 
