54 BULLETIN UNITED STATES GEOLOGICAL SURVEY. \YolY. 



fauna, i. e., lias persisted longer tlian the latter by a certain length of 

 geologic time. Applying the same reasoning to the past, I embodied 

 the idea in reference to the Laramie period ('Tort Union") in the state- 

 ment that "a cretaceous fauna was then contemporary with a tertiary 

 flora"; and, later, that "an eocene fauna was contemi^orary with a mio- 

 cene flora." It may have to be added that a miocene fauna was contempo- 

 rary with a pliocene flora. Since Mr. Lesquereux has the support of the 

 best palseobotanists of Europe, in his conclusions, it is useless to take 

 the ground assumed by a few of my colleagues, that the former gentle- 

 man has simply erred in his determinations. He gives us grounds for 

 believing that he has not done so, by giving us the European standard 

 by which his identifications are governed.* It is as follows : 



This system, it will be observed, is almost exactly identical with that 

 employed in the preceding pages as the standard of comparison for the 

 Vertebrata. Yet it has resulted, from a most careful comx)arison of both 

 faunse and florae of America with this standard scale, that two distinct 

 palceontological series have to be adopted, the one for the vertebrate 

 life and the other for the plants of the Western Continent. If this re- 

 sult be accurate, and there appears to be no avoiding it, an explanation 

 must be sought. There are only two possible ones : either the animal 

 life of North America has lagged behind that of Europe by one period 

 during past geologic time ; or, secondly, the vegetable life of America 

 has been equally in advance of that of Europe during the same period. 

 In other words, if the plant-life of the continents was contemporaneous, 

 ancient types of animals remained a period longer in i^orth America 

 than in Europe. If animal life was contemporaneous, plant-life had ad- 

 vanced by one period in Europe beyond that which it had attained in 

 l^orth America. In either case, the faunal or the floral standard of esti- 

 mation of geologic age of strata for IS^orth America is a false one, since 

 there can be but one standard of comparison for anything. But this 

 great fact being understood, the evidence of each of the great depart- 

 ments of life possesses its own intrinsic value. 



*Ann. Eeport U. S. Geol. Surv. Terrs. 1874, p. 285. 



