460 R. T. Hill — The alleged Jurassic of Texas. 



By omitting all the words of this paragraph except those in 

 italics, which he brings together and by substituting the word 

 "Cretaceous" for "Neoeomian," he succeeds. in establishing 

 his remarkable construction of a proposition which I did not 

 utter, upon which he could base his assertion that I " under- 

 took to change the age of Ammonites yo" which cannot be 

 explained otherwise than that I " wanted to sustain my classi- 

 fication of the Trinity Division in the Cretaceous, quoting in 

 his (my) favor the great D'Orbigny." These charges are repu- 

 diated by every passage referring to the species of Ammonites 

 to be found elsewhere in the volume referred to, in which I 

 repeatedly present the Jurassic affinities of this form ; but as he 

 well knows, in another paper, the species was revised by me 

 and the previous description in the work which he quoted was 

 abandoned. All the other passages referring to the age of 

 Ammonites walcotti, both in the Arkansas Report,"* and the 

 revision thereof are here reproduced in full, and I beg the 

 candid reader to compare them with Professor Marcou's state- 

 ment, in order to see if there is ground for his accusations. 



Arkansas Report, p. 125. — Reviewing the stratigrapnic evi- 

 dence afforded by Trinity formation, it seems to be clearly older 

 than any Cretaceous rocks hitherto described in this country, a 

 fact which is verified by the paleontology as shown in the next 

 chapter. 



The stratigraphic position beneath the lowest Comanche series, 

 which is of very early cretaceous (neocomian), and the extreme 

 difference in the character of the sediments and fossils, confirm 

 the opinion that the rocks are either uppermost Jurassic, lowest 

 cretaceous (Wealden) or transitional jura-cretacic. They are at 

 least older than the oldest American cretaceous rocks hitherto 

 known, and mark the littoral stages which characterized the 

 beginning of the first grand subsidence of cretaceous times. 



Proceedings of the Biological Society,f pp. 37-38: Only one 

 specimen of this species has thus far been discovered. It occurred 

 in association with 0. franklini, Vy carta lujani, Eriphyla 

 arkansaensis, and other mollusks herein described. The form 

 very much resembles in outward appearance the figures of the 

 genus Oxynoticeras of Hyatt, as given by Zittel and Steinman in 

 their Manuals, but Professor Hyatt refers it to Neumayria, and 

 contributes the following comments upon the specimen : 



"Your Ammonites walcotti is probably a Neumayria. The 

 aspect is Jurassic, but this group, Upper Jura, and the species 



* Neozoic Geology of Southwestern Arkansas. By Robert T. Hill, Assistant 

 Geologist. — Annual Report of the Geological Survey of Arkansas for 1888, vol. 

 ii, pp. 125-128. 



•f Paleontology of the Cretaceous Formations of Texas. The Invertebrate Paleon- 

 tology of the Trinity Division, by Robert T. Hill. — Proceedings of the Biological 

 Society of Washington, vol. viii, pp. 37-38, June 3, 1893. 



