FLORA OF UL1>EK rOTU.MAC FOKMAllOX. '.i^J'd 



David White and mvsolf, that tho OldcM' Potomac actually occui's in 

 Pennsylvania. 



The year 189G was the most prolihc thus f;ii' in the public discussion 

 of the natiu'e and age of the Potomac formation. The Mfteenth Amuial 

 Repoi't of the United States (ieological Sui-v(\\- contnins my paper on the 

 Potomac formation," completed and submitted in June, 1894. It was 

 soon followed by the Sixteenth Amnial Report, Part 1 of whicli contains 

 Professor Marsh's elal:)orate memoir on the dinosaiu-s of Xorth America/ 

 in which the Potomac vertebrates are described and figured; and my 

 paper' comparing the Lower Cretaceous of America, and especially the 

 Potomac formation, with the Wealden of England, the Scaly Clays of 

 Italy, and tlie Mesozoic plant-bearing deposits of Portugal. This volume 

 was in the hands of the geologists in ()ctol>er. Professor Fontaine's 

 long-delayed work on the stratigraphical relations of the Potomac 

 formation"' (see p. 358) appeared in December. It had undergone 

 extensive revision at Professor Fontaine's hands since the manuscript 

 was originally prepared in 1883, being designed as a geological introduc- 

 tion to his monograph of the flora of the Potomac formation, but not 

 used as such. The geological map was prepared imder my supervision 

 and extends from Petersburg to Baltimore. In it no attempt is made 

 to subdivide the formation. 



These works, in which the age of the Potomac formation was freely 

 discussed, with wide differences of opinion, led to a controversy in the 

 form of short articles by geologists who had paid more or less attention to 

 the subject. The unqualified assertion of Professor Marsh that the Mar}'- 

 land dinosaur bed was Jurassic, and his final position that the entire 

 Potomac formation, including the Amboy clays and the beds on Long 

 Island, Block Island,' Marthas Vineyard, etc., which I had called the 

 Island series, all belonged to that age, attracted special attention. 



« The Potomac formation, by Lester F. Ward: Fifteenth Ann. Rep. U. S. Geol. Survey, 1895, pp. 307-397, 

 pi. ii-iv. 



''The dinosaurs of North America, by Othniel Charles .Marsli: Sixteentli .\nii. Kep. V. S. (ieol. Suitpv 

 Ft. I, 1896, pp. 133-414, pi. ii-lxxxv. 



'■ Some analogies in the Lower Cretaceous of Europe and .Vnicrica, hy Lcstir I". Wiiril: Op. cit.. pp. 4(i3- 

 .542, pi. xcvii-cvii. 



''The Potomac formation in Virginia, by Wilhani .Morris Fontaine: Bull. l'. S. (Jcul. Survi'v .N'o. \4r>^ ]s'.m 

 149 pp., map. 



• Tlie geology of Block Island, by O. C. .Marsh : Am. Jour. Sci., 4th .ser., Vol. II, October, 189(), pp. 29.5-298; 

 November, lS9b, pp. 37.5-377. The Jurassic formation on the Atlantic coa.st: Ibid., December, 1896 pp 

 433-447. 



