The Surface Te/ision of Water. — Ladd. 283 
Attention has been called frequently to the function of clay 
particles in producing the phenomena of flocculation result- 
ing from their diminutive size, stress being laid upon the fact 
that as bodies decrease in size the extent of surface rapidly 
increases relatively to the mass. 
There is a point, however, of equally great importance, 
viz., that the sJiapc of the particle can almost indefinitely ex- 
tend the relative amount of surface. Thus, for a given 
mass, angular particles expose more surface than spherical 
ones. The surface of spherical bodies varies as the square of 
the diameter, but if the particles be flat, the surface can be 
increased relatively to mass, by change of shape (theoretically), 
until the molecules of the substance all lie in a single plane. 
As a matter of fact most minute mineral particles are general- 
ly angular rather than rounded. Kaolinite, however, the es- 
sential mineral of our clays, and so omnipresent, commonly 
occurs in the form of tlTin cleavage plates. It is thus prob- 
able that the diameters measured by Prof. Whitney for his 
calculation on the amounts of surface exposed in different 
soils were often the greatest diameters of flat particles, and 
consequently the amounts of such surface would be even 
greater than that indicated by him in his reports. 
Floating of Materials. 
It is not uncommon to see materials of a higher specific 
gravity than water floating upon its surface. 
The principle involved is again that of surface tension, 
and substances thus float only when attraction for the water 
is less than the value of the latter's surface tension. 
The geological results of this principle are chiefly the float- 
ing and shifting from place to place of sands. While I have 
observed such an occurrence on many occasions, in diff^erent 
places, the most important noticed was in Massachusetts, at 
the mouth of the Alerrimac river. Here the northern end of 
Plum island, which is a vast accumulation of sand, shuts in 
the harbor of Newburyport on the southeastern side. The 
action of the winds, of the waves, in time of storm, and of 
the shifting currents (the position of the harbor's channel vary- 
ing rapidly) result in the formation of numerous bays or 
"basins" in the sandy island, on the protected side, often oc- 
