From deposits of post-Glacial date abundant plant remains have been obtained, but we cannot say with any degree of certainty what proportion of these plants remained in Britain during the Ice age, and whether the greater part of the vegetation, the relics of which have been discovered in pre-Glacial beds, was destroyed or driven south by the advancing ice. We may briefly consider some of the more interesting facts brought to light by the investigation of the fossil plants in the Lower Pleistocene and Upper Tertiary beds. It is mainly to the researches of Mr Clement Reid into the vegetation of Britain immediately preceding the Glacial period, that our knowledge of this phase of the history of the British flora is due. [Illustration: Fig. 3. Pre-Glacial plants from Mundesley (A), Norfolk and Pakefield (B, C), Suffolk. (Photographs by Mr Clement Reid and Mrs E. M. Reid.) A. _Bidens tripartita_ Linn. (× 6); B. _Picea excelsa_ Linn. (nat. size). C. _Stellaria holostea_ Linn. (× 12).] On the coast of Norfolk in the neighbourhood of Cromer the sections of the cliffs reveal the existence of a succession of sands, clays, and gravels underlying Glacial deposits; this material was probably laid down near the mouth of the ancient Rhine, which in the latter part of the Tertiary period flowed across a low area, which is now occupied by the shallow southern half of the North Sea(27). The plant-fragments found in these river-sediments indicate a temperate climate. Among the plants of this pre-Glacial flora are many familiar British species, such as _Caltha palustris_ (marsh marigold), species of butter-cup, _Stellaria holostea_ (greater stichwort) (Fig. 3, C), _Bidens tripartita_ (bur-marigold) (Fig. 3, A), maple, hawthorn, the alder, hazel, the yew, Scots pine and numerous others. If, as is not improbable, these pre-Glacial plants were swept away by the subsequent arctic conditions, the great majority of them returned to their old home when a warmer climate ensued. There are however some pre-Glacial plants, such as the spruce fir (_Picea excelsa_), a cone of which is shown in Fig. 3, B, the water chestnut, _Trapa natans_ (Fig. 4), and a few other species no longer represented in the British flora. The genus _Trapa_ is a striking example of a flowering plant which has disappeared since the Tertiary period from many parts of Europe, including England, most of Sweden, and from several regions in northern Europe. It still grows in a few localities in Switzerland and in some of the Italian lakes. In pre-Glacial times the water chestnut was widely spread from Portugal and England in the west to Siberia in the east, and its hard four-pronged nuts have been recorded from many post-Glacial peat-moors in the north of Europe. [Illustration: Fig. 4. _Trapa natans_ Linn. (nat. size). From Mundesley. (Photographs by Mr and Mrs Reid.)]