ANALYSIS OF THE DAKOTA GROUP FLORA. 243 



r^eiives ot" Diospyros aw t'ouiid in different sta<j;-es ot" tlie f>enl()p-i(',al 

 fornmtious ot" Nortli America from the Ceuomauiau upwards to the pnjseut 

 epoch. Seven species of this g'euus are recognized and described in the floivi 

 of the Dakota Grroup, two of which are also found in that of Atane, and two 

 in that of Patoot. From the Michlle Cretaceous of Canada Dawson records 

 one species and one from the Upi)er Cretaceous of Vancouver Ishuid. In 

 tile flora of the Laramie (xroup, the genus has three species and the same 

 nuiul)er in that of the American Miocene. No species of Diospyros is 

 recoi'ded from any stage of the European Cretaceous and also none remain 

 in its present flora, though about twenty species have been described, either 

 from leaves or fi-om fruits and calyces from the Tertiary of that continent. 

 Tlie Persinunon, Diosjii/ms vhy/huana Linn., is tlie only species remaining in 

 the present North American flora. It reproduces in certain characters of 

 its leaves those of some of its ancestors in the Dakota Group. 



The characters of the leaves of the Ericaceae are often obscure or simi- 

 lar to the leaves of plants of other botanical divisions, therefore the references 

 of fossil leaves to particular genera of the family, or even to tlie order, are 

 often subject to criticism. As far as knowai, up to the present time, the Eri- 

 cacese are represesented in tlie Dakota Cxroup by five species of leaves of 

 Andromeda, two of Avhicli are also found in the schists of Atane. None are 

 recorded from the Upper Cretaceous, although in the Tertiary of Greenland 

 Heer has recognized five species of Andromeda and one of Vaccinium. 

 From the Laramie Group only one species is descri})ed, and from the Ter- 

 tiary measures we have three species of Anth-omeda and one of Vaccinium 

 from the Green River Group, and t^vo species of Vaccinium from the Mio- 

 cene, one of these being common to the flora of the Green River Group, 

 and one Andromeda. This is verv little, indeed, and not in accord with 

 what is known of the distribution of the Ericaceae in Europe. From the 

 Tertiary of that continent, seventy-two species distributed in eleven genera 

 have been descril)ed, the largest lunnber of them made from leaves of 

 Andromeda (Leucothoe) and Vaccinium. In the flora of our epoch, Europe 

 has only thirty species of Ericaceae, while from the Atlantic slope of the 

 United States sixty-seven species distributed in twenty-eight genera are 

 known, and from the Pacific slope forty-four species distributed in twenty 

 genera, or fifty-four species in all. Twelve of the whole number are com- 

 mon to both the eastern and the western sloj)es. From this it would appear 

 that a large number of Ericaceae, especially species of Andromeda and 

 Vaccinium, have been introduced into our flora after or during the glacial 



