ground, spreading itself over the surface and depositing a crust,
the thickness of which depended on its distance from the center
point. In this manner, in the course of time, a very flat cone is
formed, with a basin of boiling water in the middle. The continuous
deposit of dross contracts the channel, and a less quantity of water
overflows, while that close to the edge of the basin evaporates and
deposits a quantity of fine silicious earth; whence the upper portion
of the cone not only is steeper than its base, but frequently assumes
a more cylindrical form, the external surface of which on account
of the want of uniformity in the overflow, is ribbed in the form
of stalactites. When the channel becomes so much obstructed that
the efflux is less than the evaporation, the water ceases to flow
over the edge, and the mineral dross, during the continual cooling
of the water, is then deposited, with the greatest uniformity, over
the inner area of the basin. When, however, the surface of the water
sinks, this formation ceases at the upper portion of the basin; the
interior wall thickens; and, if the channel be completely stopped up
and all the water evaporated, there remains a bell-shaped basin as
even as if excavated by the hand of man. The water now seeks a fresh
outlet, and bursts forth where it meets with the least obstruction,
without destroying the beautiful cone it has already erected. Many such
examples exist. In the largest cones, however, the vapors generated
acquire such power that, when the outlet is completely stopped up,
they break up the overlying crust in concentrically radiating flakes;
and the water, issuing anew copiously from the center, deposits a fresh
crust, which again, by the process we have just described is broken
up into a superimposed layer of flakes. In this manner are formed
annular layers, which in turn are gradually covered by fresh deposits
from the overflowing water. After the pyramid of layers is complete
and the outlet stopped up, the water sometimes breaks forth on the