Chapter VIII The First Forests of Modern Type
For a long time it was believed by geologists that a great and mysterious gap separated the Upper Cretaceous from the oldest Tertiary formations; and in Western Europe, in so far as physical conditions and animal life are concerned, the severance seemed nearly complete. Oceanic deposits, like the Upper Chalk, are succeeded by beds of littoral and estuarine characters. The last and some of the greatest of the Mesozoic Saurians have their burial-places in the Upper Cretaceous, and appear no more on earth. The wonderful shell-fishes of the Ammonite group, and the cuttle-fishes of the Belemnite type, share the same fate. With the earliest deposits of the Eocene Tertiary came in multitudes of large Mammalia heretofore unknown, and the Cetaceans appear in the sea instead of the great marine lizards; while shells, corals, and crustaceans of modern types swarm in the waters. Thus it is true that a great and apparently somewhat abrupt change takes place at the close of the Cretaceous, and terminates for ever the reptilian age. Even in regions like Western America, where physically the later Cretaceous shades gradually into the earlier Tertiary, so that there have been doubts as to the limits of these several periods, the same great change in animal life occurs.
But a link of connection has at length been found in the history of the vegetable kingdom. The modern flora came in with its full force in the later Cretaceous, before the end of the reptilian age, and continued onward to the present time. Thus the plant takes precedence of the animal, and the preparation was made for the mammalian life of the Eocene by the introduction of the modern flora in the Cretaceous period. In like manner it is possible that the great graphite deposits of the Laurentian indicate a vegetation which preceded the swarming marine life of the Cambrian; and it is not improbable that the Palæozoic land flora existed long before the first land animals. Thus the plant, as in the old Mosaic record, ever appears on the day before the animal, in each stage of the development of the world.
In Chapter IV. we traced the history of the old and rich vegetation of the Coal period. But this vegetation consisted principally of cryptogams and those lowest phænogams, of the pine and cycad groups, which have naked seeds. In the modern flora we may arrange the several groups of plants, somewhat naturally, as follows:—