78 



BRITISH EOCENE FLORA. 



and the nhsence of all but the oldest of the Bournemouth types, mark out roughly the 

 age of a deposit, further distinguished, alone among Eocene floras, by the presence of 

 tree Eerns, referred by Saporta to the genera Hemitelia and Cyathea^ and interesting 

 because existing tree Ferns do not penetrate farther north than the moist valleys of the 

 Himalaya. The flora of Gelinden contains no Ferns common to our Middle Eocene, but 

 may be found to present affinities with our Lower Eocene flora. The Ores du Soissonnais 

 posssesses a flora approching that of Alum Bay, and Chrysodium Lanzoeanum is conmion 

 to it and to our liower Bagshot. The distinctly Middle Eocene types first appear in 

 France in the Eocene of Aix, many of them, however, being kept away, probably through 

 a dry climate, until the beginning of the Oligocene. Without pursuing these comparisons 

 further, it is evident that our Eocene and Oligocene Ferns appeared in a definite order, 

 and are, when contrasted with those of the rest of Europe, singularly tropical and 

 luxuriant, suggesting, indeed, that England was then situated in the line of some warm 

 current or under exceptionally favorable meteorological conditions. 



In comparing the Eocene Ferns with those of the Arctic regions, the absence there 

 of all the sub-tropical types met with in England is very striking. The absence of 

 Adiantum, for there is nothing in the Adiantites of Heer to prove affinity with Adiantum, 

 shows the nature of the climate, for one species now ranges as far north as the Jura, Tyrol, 

 and south-west of England, where it withstands considerable frosts, while others are found 

 at a height of 6000 to SOOO and even 9000 feet in the Himalayas. Equally significant 

 is the absence of the type of Pteris eocanica, for it is present in nearly all similar beds in 

 Europe and America, and is now but little less hardy Adiantum^ standing even severe 

 frost, and extending, according to Hooker, to 9000 feet in the Himalayas. Another 

 instance is seen in IFoodicardia radicans, a type of which abounded in the Tertiaries 

 of Austria, Switzerland, and America. The gradations in temperature were then, in fact, 

 as pronounced as they are in some equally separated temperate latitudes at the present 

 day. 



In comparing them with the Tertiary American Ferns, we find two even among the 

 very few yet described from the Great Lignitic series, which are certainly specifically 

 identical with our own, and these are the two oldest types. They are also accompanied 

 by representative, if not identical, species of the following European Tertiary Ferns : — 

 Sphenopteris eocmiica^ Pteris pennaformis, Woodioardia Rossneriana, Goniopteris 

 siiriaca, and Osmunda Heerii. It is thus remarkable that the Eocene Ferns of America 

 are much less tropical in aspect than those of Europe at the same period, and con- 

 sequently more resemble those of the Miocene of Europe. The temperature of the 

 western hemisphere seems to have remained colder throughout the Tertiary period than 

 ours, and hence its floras seem to have preceded ours, and present a relatively newer 

 facies. While it is just possible that these Ferns may have passed over, or descended 



1 A pinna of Osmunda lignitum was figured, 'Ann. Mag, Nat. Hist.,' ser. 4, Jan., 1869, vol. iii, pi. i,, 

 fig. 5, by Mr. A. Wanklyn, with the remark that it seemed allied to some genus of Cyathece. 



