ANALYSIS OP THE DAKOTA GROUP FLORA. 



The Flora of the Dakota Group, as far a.s it is kuowu to the present 

 time, is composed of 460 species, of which 6 are Ferns, 12 Cycads, 15 

 Conifers, 8 Monocotyledons, and 429 Dicotyledons; while that of the schists 

 of Atane,' from which 274 species are known, has 31 Ferns, 8 Cycads, 27 

 Conifers, 8 Monocotyledons, and 197 species of dicotyledonous plants, mostly 

 represented by leaves. The diversity in the number of Ferns and Conifers 

 in these floras is very striking and seems at first to disprove their reference 

 to the same age. But that disparity is merely illusive and lai-gely due to 

 local ciucumstances (to be further examined), for really, except in the Ferns 

 and the Conifers, there is little difference in the composition of the two 

 floras. That of Atane has 1 1 per cent in Ferns, while that of the Dakota 

 Group has only 1^\ per cent, with 3 J per cent of Conifers against 10 per 

 cent in Atane; the Cycads are 2f per cent of the vegetation in the Dakota 

 Group and 3 per cent in that of Atane, while the monocotyledonous plants 

 were slightly more predominant at Atane, and the Dicotyledons form 91 

 per cent of the Dakota Group flora and 72 per cent of that of Atane. 



In considering the relative distribution of the dicotyledonous plants on 

 which we have essentially to rely in looking for the degree of relationshij) of 

 the floras, we find all the essential divisions and genera of plants represented 

 in the flora of the Dakota Group and in that of the schists of Atane, and 

 among them a large number of species identical in both. 



First, the Apetalje have in both species of Myrica, Betula, Quercus, Po]?- 

 idus, Platanus, Ficus, Proteoides, Lomatia, Laurus, Sassafras, and Cinnamo- 

 mum; the Gamopetalse have in both species of Diospyros and Andromeda; 

 the PolypetaliB have species of Aralia, Hedera, Cissites, Conius, Magnolia, 

 Liriodendron, Menispermites, Sterculia, Apeibopsis, Sapindus, Celastro- 

 phylluin, Ilex, Rhamus, Juglaus, Rhus, Eucalvptus, and some Leguminosse. 

 Of the genera represented in the Flora of the Dakota Group and not in 

 that of Atane, the most important is Salix, of which abundant remains of 

 leaves and a fruiting catkin have been found in Kansas and Nebraska, 

 haviug been described by Heer, Newberry, and myself; Persea, which 



