MIOCENE FLORA. 275 



and when it becomes possible to compare the specimens of both continents, 

 identity will probably be admitted for most of them. Counting these 

 species of close affinity, it may be reasonably admitted that the relation- 

 ship of the floras is marked by one-half. At this epoch all the plan Is 

 enumerated above have disappeared from Europe, or at least are repre- 

 sented there by different specific types. 



The same degree of affinity is recognized between the North American 

 Miocene Flora and that of the Arctic in Greenland and Spitzbergen. The 

 table shows that 55 of the species are common to both. As most of these 

 Arctic species are common to Europe" also, it has been surmised that the 

 Floras of the present epoch had their origin in the north, and that from 

 there the vegetable forms have been gradually distributed southward. 

 At first this opinion seemed objectionable on account of the deficiency 

 in the Arctic Flora of southern types, which are found more marked in 

 Alaska, and still lower in the Western Territories of the United States; 

 for, until recently, the genus known as indicating the lowest degree of 

 latitude for the vegetation of the Miocene of Greenland was Magnolia, 

 This genus at the present epoch marks the northern limit of the southern 

 zone of the American Flora, reaching latitude 41° north. But now, Heer 

 describes in the Vllth volume of the Artie Flora, which has only Green- 

 land fossil plants, two species of Palms ( FlabellariaJ , four species of 

 Laurus, two of Aralia, six of Magnolia; with species of Pterospermitesi 

 Swpindus, Paliurus, &c, — indeed of most of the genera represented in the 

 Miocene Flora of southern Europe: the objection is therefore groundless. 



As yet there is not conclusive deduction from a comparison of the 

 floras of the different localities from which specimens have been obtained. 

 in regard to the relative age of the groups. 



The Alaska Flora is known by the largest number of species: it may 

 be taken for point of comparison. The different groups of California and 

 Oregon are unserviceable for that purpose, those remote localities repre- 

 senting each too few species. We therefore put in juxtaposition the 

 species of Alaska, of Carbon, of the Bad Lands, of the Chalk Bluffs of 

 California, and of the Fort Union Group. 



Alaska has 73 species, of which 13 are found in the Bad Lands, 4 at 

 Carbon, and 2 in the Chalk Bluffs. As 46 species are described from the 



