108 Marsh — Jurassic Formation on the Atlantic Coast. 



When an abstract of my communication was published, 

 although without the main illustrations shown to the Academy, 

 I received further endorsement from geologists familiar with 

 the subject, but from others, marks of disapproval pre- 

 dominated. This I had anticipated in a measure, especially 

 from the paleobotanists, whom I believed responsible for much 

 of the confusion that had so long delayed the solution of 

 similar questions, East and West. This point 1 brought out 

 in my paper, but in an impersonal manner that I hoped would 

 offend none of the craft. 



The prompt and vigorous rejoinders that even my first 

 informal announcement drew from two paleobotanists, A. 

 Hollick and L. F. Ward,* showed that I had trespassed upon 

 their bailiwick, and that some of the questions raised they had 

 settled to their own satisfaction. As their ideas in regard to 

 the value of fragmentary fossil plants as evidence of geologic 

 age differed so widely from my own and from those of many 

 paleontologists, no specific reply on my part seemed necessary, 

 and I have none to make now. Professor Ward has admitted 

 that the plants found with the vertebrates in the Potomac 

 beds of Maryland may be Jurassic, and that removes one of 

 the main points at issue between us. His words are as 

 follows : 



"If the stratigraphical relations and the animal remains shall 

 finally require its reference to the Jurassic, the plants do not pre- 

 sent any serious obstacle to such reference." (Loc. cit., p. 759.) 



That the more eastern beds may represent a somewhat 

 higher horizon, I can readily believe, but I must doubt the 

 evidence that would separate so characteristic and homo- 

 geneous a series of sands and plastic clays into two sections, 

 one Cretaceous and the other Jurassic. The few imperfect 

 plant remains that we are told authorize this separation must 

 be reinforced by other testimony to obtain even the support of 

 probability, especially when paleobotanists differ so widely 

 among themselves as to the real significance of the fragmentary 

 remains they describe. 



Next in order among my reviewers was R. T. Hill,f well 

 known for his researches in the geology of Texas, but appar- 

 ently not familiar with the typical Jurassic, East or West. He 

 evidently had not read my paper carefully, though he criti- 

 cises it at length, mainly to confirm his own conclusions as to 

 the Cretaceous age of certain deposits in Texas, which he 

 seems to imagine I do not endorse. As I. especially avoided 

 expressing any opinion on that point, or in regard to the 

 Dakota being the base of the Cretaceous in this country, as I 

 have already stated, no reply at present seems called for on my 

 part, although I hope later to refer to the question he raises 

 about the age of the so-called southern Potomac. 



* Science, vol. iv, p. 571, and p. 757, 1896. 

 f The same volume, p. 918, 1896. 



