Stevenson^] 4oJ [June 18 



teristic Cretaceous 2 and 3 are seen resting upon the sandstones. This 

 statement afforded peculiar gratification to the editor, who takes occa- 

 sion in another portion of the volume to rebuke Messrs. Marcou and 

 Heer very severely for considering these plants as Miocene. If these 

 plants are Miocene, the editor thinks the roof of our geological house 

 vras put on before the foundation was laid. This is a very proper and 

 judicious conclusion. 



Ml'. Lesquereux's rejoinder* was quite keen, defending Prof. Heer's 

 conclusion and fully endorsing it. So that he, as well as Profs. Marcou 

 and Heer regarded these plants and the including rocks as of Miocene 

 age. 



In 1863, Profs. Marcou and Capellini undertook a journey to Nebraska, 

 to effect a final determination of the question. Evidently, the testimony 

 of the plants was of little value in their eyes, for on their I'eturn they pro- 

 nounced the Dakota Group Cretaceous, and not only Cretaceous, but at 

 the base of that series as developed in America. In his work describing 

 the leaves collected by these gentlemen, Prof. Heer confessed the superior 

 value of the faunal evidence, and placed the leaves in the Cretaceous. In 

 1868, Mr. Lesquereux did the same, describing a number of Cretaceous 

 plants from the Dakota Group. In this paper he announces that a re- 

 markable generic affinity exists between the Cretaceous and Tertiary flora 

 of America. In 1874 he published a quarto volume on the Cretaceous flora 

 of the Dakota Group. It is sufficiently evident, then, that j\Ir. Les- 

 quereux regards his jjlants as affording by no means positive grounds 

 for generalization respecting equivalence of horizons in Europe and 

 America. 



Mr. Lesquereux has claimed that the determination of Miocene charac- 

 ter, made by Prof. Heer and endorsed by himself, should not be regarded 

 as in any way affecting the question of testimony, because the material at 

 their disposal was so imperfect. Such a plea is unfortunate, and the excuse 

 is worse than the erroi', if error it was. If the material was too imperfect 

 to justify a positive conclusion, why was the conclusion so emphatically 

 stated ? Either the material was sufficient, or the interpreters are untrust- 

 worthy because of rashness. That the material was sufficient is clear, 

 because the general statement of close resemblance to Tertiary forms still 

 holds good. This whole discussion very fairly exposes the value of palaeo- 

 botauy as an aid in the determination of equivalent horizons on discon- 

 nected continents. 



The plants of the Great Lignite Group are no better. Of these, Mr. 

 Lesquereux has described a great number of species. Of those identified 

 with European forms, the relations, with hardly an exception, are Mio- 

 cene, yet they are placed in the Eocene. One very eccentric feature here 

 is, that in some localities the group is Lower, and in others Upper Eocene, 

 while the stratigraphy seems to show that both epochs may belong to the 

 same horizon, and that the difference in the flora is local and synchronous, 



*Amer. Journ. Sci, Vol. 29, p. 434. 



