“…This inference is consistent with evidence provided by Cretaceous and Tertiary floras preserved in regions now semiarid to desert, as in the western United States, northern Africa, southwest Asia, Australia, and Chile. They show gradual change in time which illustrates that as rainfall diminished and longer periods of drought developed, tropical to subtropical evergreen forests were replaced gradually by drier types of tropical vegetation, culminating in the present-day thorn forest and tropical desert (Axelrod, 1950 Betula, CercidiphyUum, Liquidambar, Liriodendron, Populus, Platanus, Quercus, Salix, Sassafras, Viburnum) first appeared in the record at middle latitudes near the close of the early Cretaceous (Lesquereux, 1892;Berry, 1914Berry, , 1916a. They were associated with broadleafed evergreens in regions (Kansas, Virginia, Portugal) characterized by frostless climate.…”