134 TRANSACTIONS OF THE [jAN. 25, 



described by Prof. Hear in the Memoires de la Sociele Hclvetiqne 

 des Sciences Naturelles. 



Since that time more than one hnndred species of arborescent 

 plants have been obtained from the Dakota group, and have 

 been described by M. Lesquereux or the speaker. These include 

 oaks, maples, magnolias, sassafrases, and various other genera of 

 an aspect so modern that it is not surprising they were considered 

 as Tertiary plants. However, it is now established beyond 

 doubt that, in the middle of the Cretaceous age, a flora hardly 

 less varied than that of to-day, or inferior in botanical rank, cov- 

 ered all the central portions of this continent. 



Previous to the time mentioned, plants had been collected from 

 different parts of the Cretaceous system in Europe. From the 

 uppermost beds, a number of angiosperm leaves had been taken 

 Credneria, etc.), and from the lower portion of the system, tha 

 remains of a truly Mesozoic flora — cycads, conifers and ferns. 

 This had led to the conclusion that during the greater part of the 

 •Cretaceous age, the vegetation of the world was similar to that 

 of the Triassic and Jurassic ages. But our recent discoveries 

 in America have thrown great light on this subject, and have 

 somewhat modified the previously-entertained opinion. 



Within the last ten years, collections of fossil plants have been 

 made from the Cretaceous rocks in a large number of localities in 

 Canada and in the United States, and some of the most interest- 

 ing of all the material thus furnished has come from our own 

 immediate vicinity, from the Cretaceous clays of New Jersey and 

 Virginia. 



Combining the results of the studies of Sir William Dawson 

 of Canadian Cretaceous plants, with those obtained by M. Les- 

 quereux, Prof. Fontaine, and the speaker in the United States, 

 the development of plant life on the continent can be traced 

 with a good degree of accuracy. 



At the same time that the Cretaceous flora was studied in 

 Canada and the United States, extensive explorations and collec- 

 tions were made in Greenland. Among other material obtained 

 there were many fossil plants which were sent to Prof. Heer, 

 and described in his great work, the "Flora Fossilis Arctica,'^ 

 of which he had published seven quarto volumes before his death. 



