440 Marsh — Jurassic formation on the Atlantic Coast. 



In tlie statement 1 have quoted, I had no intention of reflect- 

 ing in the slightest degree on the work of the conscientious 

 paleobotanists who had endeavored to solve the problem with 

 the best means at their command. I merely meant to suggest 

 that the means then at their command were not adequate to 

 the solution. 



It so happened that the most renowned of European botan- 

 ists, Sir Joseph Hooker, was then in this country, and to him 

 I personally submitted the question as to the value of fossil plants 

 as witnesses in determining the geological age of formations. 

 The answer he made fully confirmed the conclusions I had stated 

 in my address. Quoting from that, in his annual address as 

 president of the Royal Society, he added his own views on the 

 same question.* His words of caution should be borne in 

 mind by all who use fossil plants in determining questions of 

 geological age, and they are especially applicable to the problem 

 now before us, — the age of the Potomac formation. 



The scientific investigation of fossil plants is an important 

 branch of botany, however fragmentary the specimens 

 may be. To attempt to make out the age of formations 

 by the use of such material is too often labor lost and 

 must necessarily be so. As a faithful pupil of Goeppert, 

 one of the fathers of fossil botany, I may perhaps be allowed 

 to say this, especially as it was from his instruction that I first 

 learned to doubt the value of fossil plants as indices of the 

 past history of the world. Such specimens may indeed aid 

 in marking the continuity of a particular stratum or hori- 

 zon, but without the reinforcement of higher forms of life can 

 do little to determine the age. 



The paleobotanists have certainly failed repeatedly in the 

 past, in attempting to define geological horizons by fossil 

 plants alone. Although they have this record as a guide, 

 some of them are still using the same methods, the same 

 material, with the same confidence, that formerly misled their 

 predecessors. In view of this, and of the great importance of 

 the present question, is it too much to ask them to reconsider 

 their verdict as to the age of the Potomac formation? 



Were the fossil plants of the Potomac that have been pro- 

 nounced Cretaceous unknown, the Jurassic age of this exten- 

 sive series would have been accepted as a matter of course long 

 ago. The strata themselves lie exactly in the position the 

 Jurassic should occupy. They agree in physical characters 

 more closely with the shallow fresh-water shales and sand- 

 stones of the Trias below, than with the deep-sea Cretaceous 

 beds above. Still more important, the animal remains taken 

 together, invertebrates and vertebrates, indicate one fauna, the 

 Jurassic. Under these circumstances, the plants alone cannot 

 finally decide the age. 



* Proceedings Royal Society of London, vol. xxvi, pp. 441, 443, 1877. 



