THE PLIOCENE FLORAS OF THE DUTCH-PRUSSIAN BORDER 147 



the various climatic changes that have intervened " ; but they add 

 that a closer study of the 147 species reveals the presence of 

 several exotic types. An investigation in 1907 by the same 

 botanists of the Rhine delta-deposits of Pliocene age of Tegelen in 

 Holland" demonstrated the occurrence of plants unrepresented in 

 the slightly younger Cromer beds, which give an Eastern facies 

 to the flora. The volume now before us is chiefly concerned with 

 a still older Pliocene flora obtained from Reuver, Swalmen, and 

 Brunssum in the province of Limburg (Holland), and over the 

 Prussian frontier. The fossihferous beds form part of the delta- 

 deposits of the Rhine and Maas, extending from the Prussian 

 frontier in the east and to East Anglia in the west. The Reuverian 

 plants were found in sediments laid down in an abandoned channel 

 or backwater, and other species were discovered in beds resting on 

 Miocene strata containing seeds distinct from the overlying 

 PUocene plants with which we are now concerned. The deposits 

 at Reuver, Swalmen, and Brunssum are probably contemporaneous, 

 and such distinctive features as are shown may be attributed to 

 geographical causes. About 300 species were recognised ; 230 

 species are assigned with " some degree of certainty " to a definite 

 position, and rather more than half the total are determined with 

 " considerable certainty." Experience has shown that fruits and 

 seeds afford in many cases trustworthy guides, and it is almost 

 entirely on their evidence that the authors' conclusions are based. 

 The occurrence of East Asiatic types in the Tegelen flora in some 

 measure prepares us for the striking resemblance exhibited by the 

 Reuverian flora to that of the mountains of West China, as also to 

 the flora of Japan, the Himalayas, and Tibet. There are, more- 

 over, indications of relationship with European floras, and to a 

 less extent wdth North American floras. In many cases where a 

 Reuverian genus is now represented in Europe and China, it is 

 with the Far Eastern species that the agreement is closest : the 

 fossil species of Pterocarya, P. limhurgensis, is nearer to P. hupe- 

 liensis of China than to P. caucasica ; Betula digitata, an extinct 

 species, is most closely allied to the Chinese species B. ulmifolia, 

 belonging to a section of the genus no longer found in Europe ; 

 the only Clematis in the Reuverian flora is C. grata, a Chinese 

 type, and not the British species C. Vitalba ; the Pliocene Ewpa- 

 torium is allied to E. japonicum, and even more closely related to 

 an unnamed variety from a mountain in Japan. The Chinese 

 species most closely related to those of the Reuverian flora do not 

 range as far north as the Pliocene stations, and they are highland 

 and not lowland forms. Picea excelsa, Quercus Bobur, Carpinus 

 Betuius, and other species recorded from the Reuverian series, are 

 either still living in Europe or are more nearly allied to European 

 species than to Far Eastern types. Other Pliocene plants, e.g. 

 Zelkoiva Keaki, Orixa japonica, Pkellodendron japo7iicum, now 

 occur on Japanese mountains ; Hehvingia himalayaca, Biicklaiidia 



* " The Fossil Flora of Tegelen-snr-Meuse, near Venloo, in the Province of 

 Limburg," Verhand. Kon. Akad. v. Wetensch. (Tweede Setie), Deel xiii, no. 6, 

 1907. 



