INTRODUCTION. 21 



comparable to this form, especially common in Nebraska; but I have seen 

 a very fine specimen of it got out of a deep tunnel in Oregon, presenting 

 upon its surface small punctiform protuberances, apparently oily glands, 

 like those remarked upon leaves of the living Rhus aromatica and other 

 species of this genus. The leaves are figured (pi. lvi, figs. 5, 6). A species 

 of Rhus is described from the Cretaceous of Greenland by Heer, while 

 considering historical authority, we have the same evidence in favor of 

 Juglans by a species of this genus in the Cretaceous Flora of Moletein and 

 one in that of Greenland. 



Of the Rosiflorece we have from the Dakota Group one leaf and one 

 fruit described as Prunus. I have recently received from M. Towner a fruit 

 of the same character upon a specimen bearing leaves of Aralia Towneri. 



The Myrtiflorce, as well as the Leguminosoe, present by a number of 

 specimens in the Greenland Cretaceous, have not been thus far positively 

 recognized in Kansas and Nebraska, but seen by one silique only in 

 Colorado. 



The few groups not considered in this review have been remarked 

 upon already in the "Cretaceous Flora," and the views in regard to the 

 leaves referred to them have not been modified either by remarks of 

 European authors or by the discovery of new materials. 



The want of positiveness in the characters of some of the Cretaceous 

 plants cannot in any way weaken reliance upon the data derived from the 

 exposition of the Flora of the Cretaceous age, nor throw any discredit on 

 the conclusions which they dictate. What the Flora of the Dakota Group 

 positively shows is a great predominance of dicotyledonous plants in its 

 composition; and that is all that may be positively known as yet of the 

 remarkable change it attests in the vegetation of that period. The causes, 

 the mode of proceeding of nature, either by slow, gradual, or by rapid 

 modifications, remains as yet inscrutable. But the characters of dicotyled- 

 onous leaves cannot be mistaken ; the relation of most of them to groups 

 of plants of the present Flora possesses positive evidence. The Oupuliferew 

 with species of Quercus and Fagus; the Salicinece with species of Populus; 

 the Platanecs with Platanus prbnceva, leaves and fruits ; the Laurinece, rep- 

 resented also by leaves and a fruit of Laurus, by leaves of Persea, Oinna- 

 momum, Sassafras; the Araliacew, the Magnoliacew, with fruits and leaves; 



