WHITE.] CATALOGUES OF FOSSILS. 265 



gin of all of tlieui were substantially the same, and yet, so far as any 

 accinnulated evidence sIioav.s, those mammalia were not i^receded in the 

 Laramie period by any related forms. Such suddenness of introduction 

 makes it almost certain that it Avas caused by the removal of some phys- 

 ical barrier, so that ground which was before potentially Teitiary be- 

 came so by actual faunal occupancy. In other words, it seenis certain 

 that those Tertiary mammalian types were evolved in some otlier region 

 before the close of the Laramie period, where they existed contemporane- 

 ously witli at least the later Laramie Dinosaurians of Cretaceous types, 

 and that the barrier which separated the faunte was removed by some 

 one of the various movements connected with the evolution of the con- 

 tinent. The climate and other physical conditions which were essential 

 to the existence of the Dinosaurians of the Laramie period having- evi- 

 dently been continued into the Tertiary epochs that are represented by 

 the Wasatch, Green Eiver, and Bridger Groups, they might doubtless 

 have continued their existence through those epochs as well as through 

 the Laramie period, but for the irruption of the mammalian horde, to 

 which they probably soon succumbed in an unequal struggle for exist- 

 ence. 



CATALOaUES OF FOSSILS. 



The following lists of fossils are those of collections which have from 

 time to time been sent to the oflice of the survey from different places in 

 the western part of the national domain by persons who are not, or 

 Avere not then, officially connected with the survey. They aie introduced 

 here partly to show the association of the species, a ])art of which were 

 originally described in publications of the survey, and jiartly to show 

 the geographical distribution of species and types, especially those of 

 Cretaceous age, in the strata of North America. 



LIST OF CRETACEOUS FOSSILS SENT BY IMK. ARTHUR LAICES FROM 

 BEAR CREEK VALLEY, KEAR MORRISON, COLORADO. 



Fox Sills Group. 



1. Pteria Unguiformis Evans & Shumard; 750 feet below the coal.* 



2. Pteria (Pseitdoptera) fibrosa Meek & Hayden ; 750 feet below the coal. 



3. Inoceramus oblongus Meek ; 750 feet below the coal. 



4. Cardium speciosum Meek & Hayden ; 200 feet below the coal. 



5. Tellina scitula Meek & Hayden; 200 feet below the coal. 



6. Mactra liolmesi Meek, sp.; 750 feet below the coal. This is the species 



which was originally described as Cyrena f and supx)osed to have 

 belonged in Laramie strata. 



7. Pachymya herseyi White; 200 feet below the coal. 



8. Dcntalium (jracile Hall & Meek; 200 feet beloAV the coal. 



0. Lunatia ocddentalis Meek «& Hayden ; 750 feet below the coal. 



10. BacuUtes ovattis Say; 750 feet below the coal. 



11. Scaphites nodosus Owen; 750 feet below the coal. 



12. iScaphites mandanensis Morton?; 750 feet beloAV the coal. This is 



recognized as belonging to the same species as the fragment which 

 was found associated with Mactra liolmesi at the original locality 

 on Ealston Creek. (See remarks under No. G of this list.) 



13. Placenticeras placenia Dekay (var.) ; 750 feet below the coal. 



* The coal rofcrred to is -vvitliin and near the base of tho Laraiuio Group, but all the 

 fossils of the list are found iu uumistakablo Cretaceous strata. 



