Dbckmbek 4, 1896.] 



SCIENCE. 



809 



slight value as witnesses of geological 

 changes. 



EVIDENCE OF FOSSIL PLANTS. 



Remains of plants are numerous, but 

 usually fragmentary, and these have been 

 collected at many localities, and studied by 

 botanists of much experience in such inves- 

 tigations. The verdict they have rendered 

 has not been a unanimous one, but is espe- 

 cially interesting, as it coincides at one 

 point with the decisions some of their 

 predecessors have rendered as to the age 

 of other geological horizons in the succeed- 

 ing formations of the West. 



The horizons I especially refer to are in 

 the Dakota, Laramie and Eocene, all es- 

 sentially of lacustrine origin, and now well 

 known. Fossil plants in good preservation 

 have been collected in each of these in turn, 

 and pronounced by eminent botanists to be 

 Miocene. Other paleobotanists of equal 

 eminence have reviewed the evidence and 

 made the age somewhat older, but, as a 

 rule, the conclusion reached made the de- 

 posits in question at least one period later 

 than the animal remains indicated. To ex- 

 plain this discordance, it was in one case 

 gravely asserted that a Cretaceous verte- 

 brate fauna lived in the midst of a Tertiary 

 flora. A larger knowledge of the facts has 

 since led to revision of the first opinions on 

 this point, and the Cretaceous age of both 

 is now admitted. 



It seems to me extremely probable that 

 in the Potomac formation we again have an 

 analogous case. The botanists have pro- 

 nounced the plants Cretaceous, while the 

 vertebrates are certainly Jurassic. Change 

 the botanical scale one notch, as was done 

 in the horizons above, and the flora and 

 fauna agree, while the Jurassic formation, 

 so long missing, is in its proper place on the 

 Atlantic coast as it is in the West. The 

 North American botanical timepiece was 

 originally set by the European clock, which 



was one period too slow, as many facts now 

 indicate. Sooner or later, an adjustment 

 must be made. 



AGE OF THE WEALDEN. 



To illustrate this, I may mention, as the 

 latest change in the European time-stand- 

 ard, the Wealden formation, the Cretaceous 

 age of which has long been considered a 

 settled point. I had studied this formation 

 at many localities in England and on the 

 Continent, as it contained a reptilian fauna 

 similar to one I had found in the Rocky 

 Mountains and regarded as Jurassic. A 

 further study of the Wealden reptiles 

 caused me to question their Cretaceous age, 

 and a comparison of these with allied forms 

 from the Rocky Mountains led me to the 

 conclusion that both series were Jurassic. 



At the meeting of the British Association, 

 at Ipswich, last year, I read a paper on 

 European Dinosaurs, including two from 

 the Wealden, and thus the question of their 

 geological age came up for determination. 

 The facts I presented, based mainly upon 

 the reptilian fauna, strongly indicated the 

 Jurassic age of the Wealden, and I urged a 

 re-examination of the question by English 

 geologists.* The subject has since been 

 taken up by Smith Woodward, with special 

 reference to the fossil fishes, on which he is 

 high authority. In the Geological Maga- 

 zine for February, 1896, he gives the main 

 results of his investigation, which prove 

 that the fishes, also, of the Wealden are of 

 Jurassic types, thus placing the geological 

 age of this formation beyond reasonable 

 doubt. 



The same conclusion, based upon a re- 

 view of the Wealden plants, has recently 

 been reached by A. C. Seward, likewise an 

 eminent authority, who states the case as 

 follows : " The evidence of paleobotany 



* Report British Association for the Advancement 

 of Science, p. 688, 1895 ■; and American Journal of 

 Science, Vol. L., p. 412, Novemher, 1895. 



