ed as
having existed in western Kentucky. It is said that around the
timberless fields there was a wide fringe of old fire-scarred trees,
with no undergrowth beneath their branches, and that as they died no
kind of large vegetation took their place. When the Indians who set
these fires were driven away, as was the case in the last decade of
the last century, the country at once began to resume its timbered
condition. From the margin and from every interior point where the
trees survived, their seeds spread so that before the open land was
all subjugated to the plough it was necessary in many places to clear
away a thick growth of the young forest-building trees.

The soils which develop on the lavas and ashes about an active volcano
afford interesting subjects for study, for the reason that they show
how far the development of the layer which supports vegetation may
depend upon the character of the rocks from which it is derived. Where
the materials ejected from a volcano lie in a rainy district, the
process of decay which converts the rock into soil is commonly very
rapid, a few years of exposure to the weather being sufficient to
bring about the formation of a fertile soil. This is due to the fact
that most lavas, as well as the so-called volcanic ashes, which are of
the same material as the lavas, only blown to pieces, are composed of
varied minerals, the most of which are readily attacked by the agents
of decay. Now and then, however, we find the materials ejected from a
particular volcano, or even the lavas and ashes of a single eruption,
in such a chemical state that soils form upon them with exceeding
slowness.

* * * * *

The foregoing incomplete considerations make it plain that the
soil-covering of the earth is the result of very delicate adjustments,
which determine the rate at which the broken-down rocks find their
path from their original bed places to the sea. The admirable way in
which this movement is controlled is indicated by the fact that almost
everywhere we find a soil-covering deep enough for the use of a varied
vegetation, but rarely averaging more than a dozen feet in depth. Only
here and there are the rocks bare or the earth swathed in a profound
mass of detritus. This indicates how steadfast and measured is the
march of the rock waste from the hills to the sea. Unhappily, man,
when by his needs he is forced to till the soil, is compelled to break
up