LEsquEREux.] PALEONTOLOGY LIGNITIC FLORA SPECIES. 421 



But where have the new types come from, and where have they origi- 

 nated? 



The climatic difference Indicated by the characters of the North 

 American Cretaceous flora, in regard to that of the Lower Lignitic, may 

 be exposed in degrees of latitude rather than by thermometrical figures 

 of an average temperature. It is about the same asthat between Ohio and 

 South Florida. In the Lower Lignitic, the palms compose a large propor- 

 tion of the flora. This family of plants is still represented in our present 

 flora by species of Chamoerops and Sahcd. But they mostly inhabit the 

 shores of the Gulf of Mexico, in South Carolina, and especially South 

 Florida. They are scarcely found inland. The highest north station of 

 Sabal is in the swamps, at the mouth of the Arkansas Biver, and here 

 it is a mere dwarf, not above one to two feet high, vegetating under the 

 deepshadeof canes and swamp-trees. With palm^ the Lignitic has 15 

 si)ecies of Ficus of a type related to subtropical forms of this genus. 

 Then Artocarpidmm, Pisona, a number of Biospyros. large-leaved species 

 of Viburnitm, llagnolia, and Dombeyopsis, with Ehamnus, species of 

 southern types. There is not, however, in the flora, any true tropical 

 form ; nor do I find any of the so-called Indo-Australian types. Cin- 

 namomum and Laurus species are more numerous than in the Dakota 

 group, but scarcely of a different type. The distribution of these two 

 genera, however, does not appear to have had a marked relation to 

 climate in the geological times. Diospyros and Magnolia are also rep- 

 resented in the Dakota group, but the forms or species are very 

 distinct and not as numerous. Many species of BJianmus of the 

 Lower Lignitic are characterized, most of them at least, by thick, 

 close secondary veins, referring these, for analogy, to the present B. 

 Carolinianus and Berchemia volubilis, whose range of distribution is 

 from Florida to North Carolina and South Arkansas. The difference 

 of temperature is, therefore, in the average, equal to that marked 

 in about 10° to 15° of latitude. It is, indeed, a small difference in con- 

 sidering the distribution of the floras of the Dakota group, and of the 

 subsequent groups of the Tertiary, and it would be easy to explain the 

 gTadual invasion of another kind of vegetation from a distance equaling 

 the 15° of latitude upon the new laud of the Tertiary, and after the dis- 

 appearance of the anterior vegetable types, if only the pre-existence of 

 such a flora was admittable. There is no difficulty to account for a 

 higher degree of temperature for the Lower Lignitic in considering the 

 flora of the Dakota group as a land-flora, or at least as a flora covering 

 the coast of an upland of wide extent, therefore under the influence of a 

 dry atmosphere. On the contrary, the Lower Tertiary land emerging 

 from an extended sea-surface, as low swamps, under a foggy or very wet 

 atmosphere, should have its climate tempered in a proportional degree, 

 and its vegetation an insular rather than a continental one. But this 

 does not explain the disappearance of the more marked vegetable types 

 of the Dakota group, and still less their re-appearance in the upper stage 

 of the Tertiary. 



The flora of the second group*, especially characterized by the plants 

 of Evanston and Spring Caiion, preserves some relation to that of the 

 first by the palms. Eemains of jflants of this family are, however, in this 

 second group, very rare,* and represent mostly fruits, which, though 

 identical with organs of the same kind found at Golden, Black Butte, 

 and the Eaton, with Sabal leaves, may, however, belong to some other 

 kind of vegetable. There is, besides, a diminished proportion of the 

 leaves referable to subtropical types. With this the second group has 



* See above : Ecmarlcs on 8j;eoie8 of the second group. 



