6 BRITISH EOCENE ELORA. 



of Godoya even more nearly resembles the Bournemouth leaf, and its presence might be 

 expected in such company. The large series of the same forms of leaves which I have 

 brought together thus greatly facilitate their determination. The limits of variation 

 in many given leaf-forms can be recognised ; leaves which would be included as varieties, 

 if found singly, are seen to be persistent in their form. Gradually the work becomes 

 easier ; to-day we have but isolated leaves ; to-morrow a chance brings to light an 

 associated fruit or flower, a branchlet of leaves, showing their attachment — some clue by 

 which conjecture is rendered almost certainty. 



In arriving at our decisions respecting the comparative ages of isolated floras, besides 

 taking into consideration those differences which are likely to be present when they are 

 widely separated, either by latitude or longitude, we must make allowance for local causes, 

 which influence and even change the character of neighbouring floras at the present day. 

 These are so well known that it is only necessary to allude to them here. Plant-remains 

 from argillaceous, and arenaceous soils would more or less differ. Limestones, serpentine, 

 and basalts have characteristic plants. Peat and soil impregnated with saline matters 

 nourish plants that are markedly dissimilar. Local differences in climate, such as are 

 caused by the prevalence of certain winds, excess of moisture, proximity to mountain 

 ranges, or to sea-currents of different temperatures, exert a powerful influence on 

 vegetation. Dificrence of altitude, it is well known, makes almost as much change in 

 each foot vertically as in miles horizontally. Some of these conditions have no doubt 

 modified the floras to be described. 



As plants of the Tertiary period are found in a more and more extended area, we see 

 that very frequently leaves, evidently of the same species, have been placed by authors in 

 many, and sometimes widely, different genera. As knowledge increases, such differences 

 will in due course become corrected. Free interchange of ideas, and, where possible, of 

 specimens before final publication, would obviate much of this burdensome synonomy in 

 the future. It would also be more dignified and satisfactory were authors of species 

 themselves from time to time to disclaim those which had become synonyms or were 

 founded on insufficient characters or data, instead of leaving others, not in so good a 

 position, to make the corrections. Eventually it is to be hoped that Botanists, who have 

 made especial orders of living plants their study, following the example so well set by 

 Mr. Hiern in his * Monograph of the Ebenaceae,' may be tempted to devote themselves 

 to a critical examination of the determinations hitherto made, so that the immense 

 importance of Plant Remains, which exceeds in many respects that of Animal Remains, 

 may be eventually conceded to them. 



Notwithstanding their importance, no section of Palaeontology has been more 

 neglected by our fellow-countrymen than the plants of the Tertiary Period. The floras of 

 our older rocks are familiar to us by the works of Lindley, Hutton, Williamson, Binney, 

 Carruthers, and others. Phillips has given us a considerable insight into the nature of 

 the British Jurassic flora ; but from Oolitic times plant-history is still, so far as this 



