Decembeb 18, 1896.] 



SCIENCE. 



921 



mands respect. On the other hand, the discov- 

 ery and description of vertebrates in America 

 has been accomplished by so little stratigraphic 

 and comparative data that the exact value of 

 these forms as aids in stratigraphic interpreta- 

 tion is uncertain. A single contribution to the 

 stratigraphy of the vertebrate beds, or critical 

 comparison of the forms with European aflfini- 

 ties, such as Prof. Ward has recently given us 

 of the plants of the Potomac formation,* would 

 be a most welcome contribution to American 

 geology. In any event, ridicule cannot over- 

 come the fact that research has not as yet 

 shown the existence in the Jurassic of dicotyle- 

 donous plants, such as the Cretaceous beds of 

 the Atlantic coast contain. 



The following statements in Prof. Marsh's 

 paper are also of interest : ' ' The inverte- 

 brates known from these strata are few in num- 

 ber, but some of the mollusks among them 

 point to the Jurassic age, as "Whitfield has 

 shown." "There is now positive proof that 

 the southern end of this series is Jurassic, and it 

 is certainly a fair conclusion that the remainder 

 is of the same age. The burden of proof will 

 rest upon those who hold to the contrary." 

 The writer has been studying the southern ex- 

 tension of the Potomac formation in Arkansas 

 and Texas for many years, but is not aware of 

 Prof. Marsh's having ever examined the beds 

 at all. There the continued Potomac beds, as 

 above stated, contain plants, vertebrates and 

 mollusks in intimate association. The counsel 

 of the ablest authorities and specialists has been 

 sought in the intei-pretation of these invertebrate 

 fossils. With the exception of Prof. Ferdinand 

 E.oemer,f and Prof. Heilprin, who maintained 

 that the beds were Upper Cretaceous, and Prof. 



*Some Analogies in the Lower Cretaceous of 

 Europe and America, by Lester Frank Ward. Ex- 

 tract from the Sixteenth Annual Report of the U. S. 

 Geological Survey, 1894-95, Part I., Director's Eeport 

 and Papers of a Theoretic Nature, 1896. 



fProf. Marsh lays stress upon the fact that Prof. 

 Roemer told him to look out for the Jurassic in 

 America. It may interest him to know that the 

 writer has a letter from Prof. Roemer, written Just 

 before his death, in which he insists upon the Upper 

 Cretaceous age of the Lower Cretaceous beds which 

 Prof. Marsh is now includins: in the Jurassic. 



Jules Marcou, who still believes them Jurassic, 

 the Lower Cretaceous position of the beds is 

 maintained by all other later authorities who 

 have studied the plants, vertebrates and inver- 

 tebrates. It is true that invertebrates are few 

 in number in the North Atlantic States, but in 

 the Texas- Arkansas region, 'the southern end 

 of this series,' which Prof. Marsh says is also 

 Jurassic, over 300 species have been noted from 

 the beds below the Dakota which, as a whole, 

 clearly testify to the Lower Cretaceous posi- 

 tions of the beds. In describing the New Jer- 

 sey forms to which Prof. Marsh refers, Prof. 

 Whitfield, instead of referring them positively 

 to the Jurassic, clearly says : ' ' We get no help 

 of sufficient value to establish the geologic 

 horizon of the beds from these molluscan re- 

 mains, and aside from the evidence furnished 

 by the plant remains we must rely entirely 

 upon their stratigraphic position."* 



It is strange that Prof. Marsh, while discus- 

 sing the invertebrates and paleobotany, makes 

 no mention of the true Lower Cretaceous verte- 

 brates, and omits them from his ' Horizons of 

 Vertebrate Fossils.' It is true that the verte- 

 brates are rare and have been less fully studied 

 than the plants and invertebrates, but Prof. 

 Cope has already described five species of fishes 

 from the Southwestern beds, and has referred 

 them all to the Cretaceous. Willistonf has 

 likewise published several vertebrates from the 

 Lower Cretaceous of Kansas, including turtles, 

 fishes, saurians and crocodiles. 



Prof. Marsh's views of continuous sedi- 

 mentation along the Atlantic coast through the 

 various periods of geologic time are also pecu- 

 liar. He says : "To place the strata in ques- 

 tion in the Jurassic section of the Atlantic 

 coast at once removes many difficulties that 

 have hitherto perplexed students of the Meso- 

 zoic of this region. It completes the series, 

 and shows in part at least what was done in 

 deposition during that long interval between 

 the end of Triassic and the beginning of Creta- 

 ceous time." It is not exactly clear how the 

 geologic series of the Atlantic coast will be 

 completed by restoring the Jurassic sediments, 

 as he proposes to do, at the expense of the 



* Monograph IX., U. S. Geol. Survey, p. 23, 1885. 



t Kansas University Quarterly, July, 1894. 



