A REPORT ON THE CRETACEOUS FOSSILS CONTAINED IN THE 

 COLLECTIONS BROUGHT FROM NEW MEXICO BY THE EXPLOR- 

 ING EXPEDITION UNDER THE COMMAND OF CAPT. J. N. MA- 

 COMB, OF THE UNITED STATES TOPOGRAPHICAL ENGINEERS. 



HY V. I?. MKKK.* 



The following pages and the accompanying plates contain descriptions and illus- 

 trations of eleven new species of Cretaceous fossils. Figures and descriptions have 

 also been added of a few previously known forms, of special interest as guides in iden- 

 tifying the several formations, and in determining their relations to established horizons 

 in the same system elsewhere. 



By reference to the able report of Dr. Newberry, the geologist of the expedi- 

 tion, it will be seen that he divides the Cretaceous rocks of New Mexico into three 

 groups, as follows: 



1. THE UPPER DIVISION, consisting of gray, white, and purple marls, alternating 

 with soft, yellow, calcareous sandstone, altogether 1,500 feet in thickness. In this 

 group, a portion of which he thinks may possibly prove to be of Tertiary age, he 

 observed numerous silicitied trunks of trees, together with leaves of Alnus, Platanus, 

 &.c. At the base of the whole, he found a thin bed containing Placenticer as placenta,^ 

 Utirit/itrx iD/cfjts, rar., Aiiclntra, Inocerantus, &c. 



2. THE MIDDLE DIVISION is composed of dove-colored and ferruginous limestones, 

 shales, &c., altogether from 1,2 00 to 1,500 feet in thickness, and containing Prionocyclus, 

 Mtiroiitlii, Sccijtli/tcs larnrformis, Inoccramus problematic us, Ostrca congcsta, &c. 



3. THE LOWER DIVISION, consisting of yellow or brown sandstone and green shales, 

 250 to 400 feet in thickness, containing Ammonites, Exogyra, Plicatula, and leaves of 

 Salix, PlatamiSj Qucrcns, (fee- 

 After a careful examination of the specimens from these rocks, I fully concur with 



Dr. Newberry in the opinion that all of those of the Lower Division, with possibly 



* This report was prepared in 1860, and has remained unpublished until this time (November, 1875). I have at 

 tliis latter date given it as careful a revision as numerous other engagements would permit ; and, in doing this, several 

 changes of nomenclature were found to be necessary, in order to bring the whole up to the present more advanced state 

 of palwontological science. Such changes as refer to other publications issued at any date after that first above incn- 

 t iom-d, were of course made in the revision of the MS. at the latter date. F. 15. M. 



tThe name I'lacenticrras was first proposed by me in the Proceedings of the Philosophical Society of Philadelphia, 

 1.-VH ; and again used in Haydon's Second Annual Report of the United States Geological Survey of the Territories, 297, 

 1872 ; also in Upper Missouri rain-ontology, now in the press (November, 1875). Ammonihs placenta, Dekay, is the type 

 of the gronp. 



10 S F 



