[Illustration: SLOW INFLUENCES THAT DESTROY IN ONE PLACE AND BUILD UP IN ANOTHER The coming of the sea over the land is so slow as to be almost imperceptible, but these pictures illustrate its progress. The pictures in the upper half of the page show how the sea is encroaching on the coast; the opposite result is shown in the bottom view from Reigate Hill, where we see an ancient arm of the sea now a rich and populous valley. ] Among the forces which we find attended by a transformation of the fauna and flora of the earth’s eras, the influences of climatic changes in particular are clearly and surely shown. In that primeval period in which the coal group was formed the climate in widely different parts of the earth was comparatively equable, little divided into zones, and of a moist warmth; this is proved by the really gigantic masses of plant growth implied by the formation of many coal strata, in which the remains of a luxuriant cryptogamic flora are everywhere embedded. In Greenland, in the strata belonging to the chalk period, and even in the deposits of the Tertiary Period, which immediately precedes the Drift Era, the remains of higher dicotyledonous plants of tropical character are found. The occurrence of palæozoic coral reefs in high latitudes also goes to prove that the temperature of the sea water there was higher at that time: in fact, that a tropical climate existed in the farthest north--an extreme contrast to the present ice-sheet on its land and the icebergs of its seas. [Illustration: EUROPE BEFORE THE BRITISH ISLES WERE FORMED This map and section illustrate the coast line of Prehistoric Europe when the British Isles were part of the Continent and the North Sea did not exist. The black parts of the section were all above the level of the Atlantic. ] [Illustration: THE SUBMERGED LANDS OF EUROPE This map and section show how the Continental shelf of Europe runs out to the Atlantic, and how enormous is the area now submerged in the comparatively shallow water of the North Sea, the Irish Sea, and the Channel. ]