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.
Fig. 4. Trapa natans Linn. (nat. size). From Mundesley. (Photographs by Mr and Mrs Reid.)
From the so-called Cromer forest-bed and associated deposits on the Norfolk coast several pre-Glacial plants have been obtained, indicating a temperate climate during this phase of the Pleistocene period. A few arctic species, such as the dwarf birch and arctic willow obtained from the deposits next above the Cromer forest-bed, herald the near approach of glacial conditions.
It may be remarked in passing that no satisfactory evidence has been discovered in Britain of the existence of man in this part of Europe in pre-Glacial days: it is, however, believed that flints from Tertiary strata on the continent show traces of human workmanship. As Sir Edwin Ray Lankester said in 1905, 'It is not improbable that it was in the remote period known as the Lower Miocene—remote as compared with the gravels in which Eoliths [primitive stone implements] occur—that Natural Selection began to favour that increase in the size of the brain of a large and not very powerful semi-erect ape'([28]).
Though comparatively recent in terms of geological chronology, the remoteness, according to ordinary conceptions of time, of the Tertiary period is brought home to us when we endeavour to grasp the fact that it was during this chapter in the earth's history that some of our highest mountain-ranges, such as the Alps, the Carpathians, and Himalayas were formed by the uplifting of piles of marine sediments. From Tertiary strata in the Isle of Wight, on the Hampshire coast, and in the London basin numerous fossil plants have been obtained, which afford convincing evidence of climatic conditions much more genial than those of the present day. The presence of palm leaves and of a wealth of other sub-tropical plants in Lower Tertiary beds in England reveals the existence of a flora differing considerably both from that in the uppermost Tertiary beds of Norfolk and from the modern British flora, but closely allied to the present Mediterranean flora.
The basaltic columns of the Giants' Causeway and of the Staffa Cave, and the terraced rocks which form so characteristic a feature in the contours of the Inner Hebrides, are portions of lava-flows, which in the early days of the Tertiary period were poured out over a wide area of land stretching from the north-east of Ireland, through the Western isles of Scotland, the Faroë islands, to Iceland and Greenland. While in this northern region volcanic activity was being manifested on a stupendous scale, a shallow sea extended over part of what is now the south-east of England in which was deposited a considerable thickness of sedimentary material derived from the neighbouring land. In this upraised sea-floor, known as the London clay, which is exposed in the Isle of Sheppey and in many other localities, numerous fossil fruits and fragments of wood occur in association with marine shells. The fact that many of the fruits were ripe at the time of their entombment led some eighteenth century writers to assign an autumn date to the universal deluge. One of the Sheppey fruits may be mentioned as an especially interesting sample of the early Tertiary flora, namely the genus Nipadites, so named from the very close resemblance of the fossils to the fruits of the existing tropical plant Nipa. Nipa fruticans, sometimes described as a stemless palm because of the absence of the erect stem which is usually a characteristic feature of palms, grows in brackish estuaries of many tropical countries ([Fig. 5, A]): it has long leaves not unlike those of the date-palm and bears clusters of fruits as large as a man's head; a single fruit is two or three inches long and its hard fibrous shell is characterised by four or five longitudinal ribs ([Fig. 5, B]). The fruits of Nipa, which may be carried a considerable distance by ocean-currents without losing the power of germination, are constantly found with other vegetable drift on the beaches of tropical islands. The discovery of fruits of Nipa (or Nipadites), hardly distinguishable from those of the existing species, in Tertiary beds in England, Belgium, in the Paris basin, and in Egypt affords a striking instance of changes in the geographical distribution of an ancient plant now restricted to warmer regions.