erature that it has at the present
time--an age when vegetation was forced by the internal heat of the
earth instead of having to receive all its warmth from the sun's rays as
we do now. Some of our readers are familiar with what is commonly termed
a hotbed. A hotbed is made by putting soil on top of substances that
will ferment and create heat underneath the soil. This heat from beneath
will force vegetation and cause a much larger growth than there will be
if left to the sun's rays alone. During the carboniferous age the earth
was a great hotbed.

The fossils of trees and plants, as well as reptiles, that we find in
the great coal measures of the world, show that they were of large
tropical growth, and this is shown not only in the temperate zone, but
in the zone farther north. For ages and ages this rank growth of
vegetation grew up and fell down until a great layer of vegetable matter
was formed, which at a later time was covered over by other
stratifications of earth material, so that these great layers of
vegetable formation were hermetically sealed and pressed down by an
enormous weight that increased as time went on. The formation of coal
may be studied even at this day (for it is now going on) by visiting and
examining the great peat beds that are found in various parts of the
world. It is well known that peat is used as a fuel by many people,
especially the peasantry of the old countries. If peat is pressed to a
sufficient degree of hardness it burns in a manner not unlike some forms
of coal. Peat is a vegetable formation and has been formed by the rank
growth of various kinds of vegetation in swampy places. Of course, it
lacks the purity of the coal that was formed during the carboniferous
age, because of the much slower growth of vegetation now than during
that time, and the opportunity that peat bogs offer for an intermixture
of earthy with the vegetable matter. The fact that we find the imprint
of trees and ferns and other vegetable growth of tropical varieties, as
well as the fossils of reptiles, imbedded in the coal measures, proves
that at one time this stratum was at the land surface of the earth. We
also find that all of the formations of the Secondary and Tertiary
periods are on top of the coal--and this shows that after the age of
rank vegetable growth there was a sinking of the earth in many places
far down into the ocean--so that vast layers of rock formed on top of
these beds of vegetable matter.