Submerged Forests.—
Evidence of change in the coast-line is shown by the occurrence of submerged forest-land, known as “fossil forests,” which consist of the stumps of trees still embedded in the black, loamy soil. Such forests, when of comparatively recent age, are found near the existing coast-line, and may sometimes extend for a considerable distance out to sea ([Fig. 9]).
From the foregoing we learn that:—
1.—Fossils afford data of the various Changes that have taken place in past times in the Relative Positions of Land and Water.
Changes of Climate in the Past.—
At the present day we find special groups of animals (fauna), and plants (flora), restricted to tropical climates; and others, conversely, to the arctic regions. Cycads and tree-ferns, for example, seem to flourish best in warm or sub-tropical countries: yet in past times they were abundant in northern Europe in what are now temperate and arctic regions, as in Yorkshire, Spitzbergen, and Northern Siberia, where indeed at one time they formed the principal flora.
The rein-deer and musk-sheep, now to be found only in the arctic regions, once lived in the South of England, France and Germany. The dwarf willow (Salix polaris) and an arctic moss (Hypnum turgescens), now restricted to the same cold region, occur fossil in the South of England.
In Southern Australia and in New Zealand, the marine shells which lived during the earlier and middle Tertiary times belong to genera and species which are indicative of a warmer climate than that now prevailing; this ancient fauna being like that met with in dredging around the northern coasts of Australia ([Fig. 10]).