1870.J 4:0i [Stevenson. 



the same extent. As it is, tliey are of some local service. The flora of 

 the Dakota Group serves to identify that formation at many localities, 

 east from the Rocky Mountains when the rock is barren of animal re- 

 mains. The position of this flora has been fixed by means of its position 

 in and below rocks containing the ordinary Cretaceous types of animals. 



But why do we call one flora, Cretaceous, or another Triassic, or a 

 tliird, Tertiary ? Simply because it is found in rocks belonging to such 

 a group. Let it not be forgotten that we do not call the group Creta- 

 ceous, or Tertiary, because of the flora. Stratigraphy determined the 

 general succession of rocks ; animal life determined the division into 

 groups. 



The floras of our later geological eras cannot afford a satisfactory basis 

 for generalizations looking to a determination of equivalent horizons in 

 Europe and America. The conditions on the two continents were widely 

 different. This general statement has been practically accepted as true 

 by our palseo-botanists, Dawson, Lesquereux, and Newberry, all of whom 

 have acknowledged that the testimony of plants is inferior to that of in- 

 vertebrates. This story is a brief one. 



In 1858, Mr. Meek and Dr. Hayden submitted to Dr. Newberry a col- 

 lection of dicotyledonous leaves which they had obtained from the Da- 

 kota Group, of Nebraska. Dr. Newberry found great resemblance 

 between these and the Tertiary flora of Europe, but regarded them as of 

 Cretaceous age, being convinced by the stratigraphy and the testimony 

 of invertebrate remains in the overlying rocks. Sketches of some of 

 these were sent to Prof. Heer, who, in a letter to Mr. Lesquereux,* very 

 positively asserted that Newberry erred in his conclusions, and that the 

 plants are all of Tertiary forms. His language is as follows : 



"It is true that I have seen only some drawings which were sent to me 

 by Messrs. Hayden and Meek, but they are all Tei'tiary types. The sup- 

 posed Credneria is very like Populus leuce, Ung. of the Lower Miocene, 

 and the Ettinghausiana seems hardly rightly determined. Besides, it is 

 a genus badly founded, and as yet has no value. All the other plants 

 mentioned by Dr. Newberry, belong to genera that are represented in the 

 Tertiary and not in the Cretaceous. And it is very improbable that in 

 America the Cretaceous flora had the characteristic plants of the Tertiary^ 

 and this would be the case if these plants did belong to the Cretaceous." 



To this the editors of the Journal append a note, stating that similar 

 leaves had been collected by Prof. Cooke, from the base of the Creta- 

 ceous, as well as by Dr. Newberry, from the same horizon, in New 

 Mexico, so that if the leaves are Tertiary, our Cretaceous is abolished. 



Dr. Newberry replied,! stating that he had collected such dicotyledon- 

 ous leaves from the Lower Cretaceous sandstones at Galisteo Creek, in 

 New Mexico, where the Upper Cretaceous sandstones also are exposed, 

 and at various localities further east to the Canadian river where charac- 

 *.'lmer. Journal of Sci., 2(1 series, Vol. 28, p. 88. 

 . fAmer. Journ. Sci., Vol. 29, p. 299. 



