MEDIAEVAL OR MESOZOIC TIMES. 183 



pressions to Prof. O. Heer, of Switzerland, who complicated the 

 discussion still more by pronouncing them to he of Tertiary age." 

 Hayden himself had reported on the peculiar character of this group 

 as early as 1853. In 1856 and 1857, assisted now by Meek, he re- 

 sumed the study of this deposit in Kansas as they had previously 

 done in Nebraska, and both reaffirmed the conviction which Hayden 

 had previously expressed, that these rocks were of Cretaceous age. 

 Dr. Newberry expressed the same conviction when their whole 

 collection of leaves was submitted to him. This reference of these 

 leaves to the Cretaceous, first by Hayden, and then by Meek and 

 Newberry, produced a difference of opinion and much discussion 

 among some European and American geologists. Dr. Newberrv 

 has given the details of this discussion in his "Extinct Floras." To 

 settle the question of the geological age of the Dakota Group, 

 Professors Capellini, of Paris, and Marcou, of Dresden, visited Ne- 

 braska and examined the stratiography of this group and collected 

 the fossil leaf impressions which it contain*, all of which were af- 

 terwards submitted to Prof. O. Heer for examination. In his 

 report Phyilites ttu Nebraska seventeen new species were de- 

 scribed with illustrations. In this report Prof. Heer admitted the 

 accuracy of Hayden's original reference of this deposit to the Cre- 

 taceous. Capeliini and Marcou also on stratiographical evidence 

 came to the same conclusion, and admitted that they w r ere much 

 less successful than the American geologist, as they, unlike him 

 were unable to discover the line of junction with the next group 

 above. It therefore became settled in the minds of the eminent 

 European and American geologists, who had especially investigated 

 the matter, that the Dakota Group was the basal member of the 

 Cretaceous in this region, and was the equivalent of the middle or 

 lower part of the upper of the European Cretaceous. 1 have given 

 this outline because, even yet, in the minds of some geologists who 

 have not studied the history of these investigations there is a doubt 

 about the cretaceous reference of this group.* It should also he 

 remembered to the credit of Dr. Hayden that he was the first to 

 outline, to name, and to ascertain the true position of this group. 



Fossil Leaves of the Dakota Group. As early as 1853 Dr. 

 Hayden had obtained impressions of dicotyledonous leaves from the 

 rocks, which he subsequently named the Dakota Group. They 

 were remarkable for their modern aspect, as most of the genera 



*See on this subject Lesquereux's Dakota Group Cretaceoua Flora. 



