262 [Proc. B. N. F. C, 



as Madeira and England are to each other now, being at the 

 same relative distances, and with the same relative temperatures, 

 and exhibiting similar differences in their floras. There is thus 

 every physical ground for believing that the Greenland Tertiary 

 plants are more likely to be Eocene than Miocene. 



Now, what is the evidence of the plants themselves } There 

 is a total absence, in the first place, of any characters among 

 them which would preclude their being referred to the Eocene. 

 The fact that a proportion of them had been identified by Heer 

 with those of the Swiss Miocenes, may be set against the consi- 

 derable number which are equally identified with plants of the 

 undoubted Eocene Lower Lignitic series of America, and a 

 number of forms in the latter again with those of the Miocene 

 of Switzerland. The truth is, that at present any formation 

 containing Dicotyledons may be with almost equal plausibility 

 referred to any age an author pleases, for besides the similarity 

 always existing between the ordinary forms of ovate and lanceo- 

 late leaves, many species, no doubt, actually had a great range 

 in time, and occur with slight modifications from the Cretaceous 

 to the Miocene inclusive. The existing confusion originated in 

 a very simple manner. The flora of Oeningen must be accepted 

 as a very typical Miocene flora, containing possibly, scarcely 

 any Eocene forms. It contains, however, many plants common to 

 somewhat older floras, which do contain a percentage of Eocene 

 forms. The only series from undoubted Eocenes formerly avail- 

 able for comparison were peculiar, and therefore misleading; 

 I allude to the floras of Alum Bay and Sheppey. In the 

 absence of stratigraphical evidence the known Miocene types 

 decided the question of age, and the unknown Eocene types 

 became incorporated into and in their turn typical constituents 

 of Miocene floras, and were used to identify yet older beds, with 

 still more Eocene affinities, as Miocene, so that at last every bed 

 containing a dicotyledon was pronounced by Heer to be Mio- 

 cene, until as I have said, even a parcel of plants from the 

 American Cretaceous was returned with the positive assurance 

 that they were Miocene. Heer did not possess the data requi- 



