In England great chalk beds crop out in
cliffs on the southern coast, and, as we have seen, these chalk rocks
are largely made up of the shells of marine animals. London stands on a
chalk bed, from six hundred to eight hundred feet thick. Indeed, England
has been poetically called Albion, White-land, from this appearance of
her coast.

All of the great chalk beds were formed ages after the coal beds, as the
latter are found in the upper strata of the Paleozoic period.

A study of these strata will show that there are many layers of coal
strata varying in thickness and separated by layers of shale and
sandstone. How the shale and sandstone layers are formed will be the
subject of a future chapter.

From the position that the coal measures occupy, being entirely under
the Secondary and Tertiary formations, it will be observed that they are
very old. If we should examine a piece of ordinary bituminous coal we
should find that there are lines of cleavage in it parallel to each
other, and that it is an easy matter to separate the lump on these
lines. If we examine the outcrop of a coal bed we will find that these
lines of cleavage are horizontal. This indicates that the great bulk of
vegetable matter of which the coal formation is made up has been
subjected to tremendous pressure during a long period of time. If we
further examine the structure of a body of coal we find the impressions
of limbs and branches as well as the leaves of trees and various kinds
of plants. We shall further find that these impressions lie in a plant
in the same direction as the line of cleavage. This is a point to be
remembered, as it helps to explain the nature and structure of other
formations than those of coal. Not only are leaves and branches of
vegetable matter found, but fossils of reptiles, such as live on the
land. Sometimes there is found the fossil of a great tree trunk standing
in an erect position, with its roots running down into the rock below
the coal bed, while the trunk extends upward entirely through the coal
and high up into the other strata. All of these facts lead us to the
firm conclusion that when the trees were grown that formed these beds
they were above the surface of the ocean. This, taken in connection with
the fact that the vegetable fossils that are found indicate a tropical
growth of great size, drives us to the conclusion that the climate at
the time these coal measures were formed was much warmer than it is now.