ANALYSIS OF THE DAKOTA GROUP FLORA. 255 



the so-called ligiiitic strata of the Yellowstone River. In tlu; Green River 

 Group we have one Amelanehiei', one Crataegus, one Rosa, and one Ani}^g- 

 dalus, and from the Miocene strata I have described one Cratajgus from 

 Carbon, Wyoming, one Spiraea from Alaska, one Prunus from the Bad 

 Lands, and one Cercocarpus from the auriferous gravel deposits of Cali- 

 fornia. Heer records fourteen species of Rosacea^ in the Arctic Tertiary. 



The Leguminospe, which are richly represented now in the vegetation 

 of om* globe, are as yet recognized in the Cretaceous merely liy detached 

 leaflets, whose generic relations remain uncertain. This oi'der being essen- 

 tially composed of herbaceous plants with compound leaves, with the 

 pimiules easily detached, specimens have frequently been preserved as fos- 

 sil witnesses of its ancient origin. Heer has found in the schists of Atane 

 seventeen species of Leguminosae, while ten have been described from the 

 Dakota Group. Of these one is I'epresented by a large legume, whose 

 generic relation is still unknown. 



Besides the plants to which the above remarks are applicable there are, 

 in the flora of the Dakota Group, a number of vegetable remains whose 

 relation to any of the vegetable groups, orders, or genera, admitted in the 

 flora of the present epoch, has not been recognized. These plants, described 

 luider peculiar generic names (Protophyllum, Aspidiophyllum, Eremophyl- 

 lum, Anisophyllum, etc.), may represent short-lived types whose disappear- 

 ance is far more easily explained than their origin. For, indeed, their 

 essential characters may have been gradually eftaced by rapid modification 

 and so intimately mixed with others that tliey have become unrecognizable; 

 or, under adverse influences may have become really extinct as races unfit 

 to remain associates of those of the future. 



It is well to remark, also, that though some types of the Cenomanian, as 

 shown by the leaves of the Dakota Group, generally remain distinct and 

 plainly defined in the vegetation of some of the subsequent geolog'ical for- 

 mations, the chain of evidence is not always continuous. A number of 

 these, for example, still remain unrecognized in the Upper Cretaceous, though 

 present in more recent strata of the Laramie or of the Tertiary. We know 

 very little as yet of the flora of the Senonian or of intex'mediate stages 

 between the Dakota and the Laramie Groups. But judging from recent 

 discoveries in Wyoming, Montana, Canada, and Vancouver Island, we have 

 been al)le to recognize in the scantv materials obtained the presence and 

 therefore the persistence of some of the primitive or more ancient types, and 

 it is most probable that further research will complete the evidence of the 



