As already remarked, this extra warmth came from the earth itself before
it had cooled down to its present temperature, rather than from the heat
of the sun. There is nothing inconsistent in the thought that the sun
may have been warmer in a former age than now. We may conceive that the
earliest coal formations took place when the land stood above the
surface of the water, and that the conditions were favorable for a rapid
and luxuriant growth of vegetation; after this had gone on for a very
long period of time, by some convulsion of nature the land surface was
submerged under the ocean, when other mineral substances were deposited
on top of this layer of vegetable growth, which hardened into a rock
formation. At a later period the earth was again elevated above the
surface of the water and the same process of growth and decay was
repeated. These oscillations of the earth up and down occurred at
enormously long intervals, until all of the various coal strata with
their intermediate formations were completed. After this we must suppose
that the whole was submerged to a great depth and for a very long period
of time, because of the great number and various kinds of rock
formations laid down by water that lie on top of the coal measures. This
tremendous weight, as it was gradually builded up, subjected these
vegetable strata to an inconceivable pressure. In some places this
pressure was much greater than in others, which undoubtedly is one of
the reasons why we find such differences in the structure and quality of
coal. There were no doubt many other reasons for differences, one of
them being the character of the vegetable growth out of which they were
formed. Again, in some parts of the world these coal strata may have
been subjected to a considerable degree of heat, which would change the
structure of the formation, and in some cases drive off the volatile
gases. One can easily imagine that heat was thus a factor in the
formation of what is known as anthracite coal, so much less gaseous than
the bituminous kinds. The anthracite beds seem to be denser and of a
more homogeneous character. The lines of cleavage are not as prominent,
but there are the same evidences of vegetable origin that we find in the
bituminous formations.

It will be seen from what has gone before that coal was first wood. But
wood is a product of sunshine. Thus the sun was the architect and
builder of the trees and plants that were finally hermetica