GEOLOGICAL SURVEY OF THE TEERITORIES. 317 



Some other groups of plants represented in the Tertiary flora of Eu-. 

 rope, and without representatives in our i:)resent flora, are not seen, as 

 it has been remarked already, in the North American Cretaceous and, 

 Tertiary, the Froteacece, the Myrtacew, for example. The total absence 

 of a group which, like that of the Froteacex^ has, in the Miocene flora of 

 Europe, thirty-five species, is the best proof we may have of the homo- 

 geneity and indigenous origin of our flora. Shall 1 say of its antiquity 

 too ? Facts seem to indicate for our flora, as for our race, a northern 

 origin. Our types may have risen in Greenland and gradually passed 

 southward, some of them branching to Europe. But as these types of 

 old have been preserved to us only, we may at least admit what Agas- 

 siz calls " the more ancient character of our flora, which bears the mark 

 of former ages, a particularity which agrees with the geological struc- 

 . ture, and indicates that this region Avas a large continent long before 

 extensive tracts of land had been lifted above the level of the sea in any 

 other part of the world." * 



Summary. 



The recapitulation of the essential data pointed out by the examina- 

 tion of the Tertiary and Cretaceous specimens of Dr. Hay den's collec- 

 tion of fossil plants presents the following conclusions : 



1st. The Tertiary flora of North America is, by its types, intimately 

 related to the Cretaceous flora of the same country. 



2d. All the essential types of our i^resent arborescent flora are already 

 marked in the Cretaceous of our continent, and become more distinct 

 and more numerous in the Tertiary ,• therefore the origin of our actual 

 flora is, like ii^facies^ truly North American. 



3d. Some types of the North American Tertiary and Cretaceous flora 

 appear already in the same formations of Greenland, Spitzbergen, and 

 Iceland ; the derivation of these types is therefore apparently from the 

 arctic regions. 



4th. The relation of the North American Tertiary flora with that of 

 the same formation of Europe is marked only for North American 

 types, but does not exist at all for those which are not represented in 

 the living flora of this continent. Therefore the European Tertiary flora 

 partly originates from North American types, either directly from our 

 continent or derived from the arctic regions. 



5th. The relation of the Tertiary flora of Greenland and Si^itzbergen 

 with ours indicates, at the Tertiary and Cretaceous epochs, land con- 

 nection of the northern islands with our continent. 



6th. The species of plants common to the Cretaceous and Tertiary 

 formations of the arctic regions and of our continent indicate, in the 

 mean temperature influencing geographical distribution of vegetation, a 

 difference, in -f, equal to about 5^ of latitude for the Tertiary and Cre- 

 taceous epochs. 



7th. The same kind of observations on the geogTaphical distribution 

 of vegetable species shows at the Tertiary and Cretaceous times difier- 

 ences of temperature according to latitude, analogous to what is remarked 

 at our time by the characters of the southern and northern vegetation. 



To these important conclusions, the examination of Dr. Hayden's 

 specimens indicates some of the essential points which should be taken 

 into consideration for directing future researches: 



1st. As we have not yet suilicient ])oints of comparison between the 

 fossil flora of the eastern and that of the western slopes of our continent, 



*Lakc Superior, its i)bysical character, &c., by L. Agassiz, p. 150. 



