6 



Eeptilia — 



Dinosauria 1 



Fterosauria 4 



Sauropterygia 3 



Testudinata 3 



PytJionomorpha 27 



Pisces — 



Isospondyli 31 



Selachii 10 



IV. The Pierre group ; in Nebraska, and Dakota, and Middle Colo- 

 rado, south of tke divide between the waters of the Arkansas and Platte 

 Eivers. Also the lower bed of Greensand of ]S"ew Jersey. Besides the 

 numerous remains of reptUes and fishes found in K"ew Jersey, this for- 

 mation contains saurian (mosasauroid) remains in Colorado. Weber 

 River, Wyoming,* below the coal. 



V. The Fox Hills group ; extended in Central Dakota ; on the Ar- 

 kansas and tributaries in Southern Colorado ; and as the second Green- 

 sand bed in New Jersey.t 



YI. The Fort Union or Lignite group. 



With this epoch we enter debatable ground, and begin to consider 

 strata deposited in brackish or fresh waters, which were more or less in- 

 closed by the elevation of parts of the Eocky Mountains and other 

 Western regions, and which are therefore more interrupted in their out- 

 lines than the marine formations which underlie them. Dr. Hayden 

 has recognized and located a number of formations of this character, to 

 some of which he has applied the name of " transition beds." That the 

 period of their deposit was one of transition from marine to lacustrine 

 conditions is evident, and that a succession of conformities in position 

 of beds may be traced from the lowest to the highest of them, and with 

 the Tertiarj"^ strata above them at distinct localities, beginning at the 

 south and extending to the north, is also j)roven by Hayden and others. 

 It appears impossible, therefore, to draw the line satisfactorily without 

 the aid of paleontology 5 but here, while evidence of interruption is clear, 

 from the relations of the plants and vertebrate animals, it is not identi- 

 cal in the two cases, but discrepant. I therefore append a synopsis of 

 the views expressed by authors, with a presentation of the evidence 

 which is accessible in my department. I am aware that the combination I 

 shall make is of a highly inflammable character, because it not only re- 

 lates to the most combustible deposits of the West, but also to the 

 .''partie houteuse" of cotemporary geologists and paleontologists. But 

 should any inflammation ensue, I hope it will be attributed to the nature 

 of the materials employed, rather than to any inattention on the part of 

 the author to the just claims of his friends. 



Hayden has named the following as distinct epochs of transitional 

 character, all of which he originally referred to the Tertiary period. I 

 give them in the order of age which he has assigned to them.* (1.) Pla- 

 cer Mountain ; locality, New Mexico. (2.) Canon City coals. Southern 

 Central Colorado. (3.) Fort Union, or Lignite group; Dakota, Montana, 

 and Wyoming. (4.) The Bitter Creek series; embracing the Bitter 

 Creek coals, Wyoming. (5.) Bear Eiver group, Western Wyoming. To 

 these may be added the Judith Eiver beds, of Montana, which Dr. Hay- 



* Hayden's Anniial Report, 1870, p. 167. 



tFor a review of the extiuct reptiles of this epoch, see the author's Extinct Batrachia 

 EeptiJia, etc., N. Am., 1870. 

 *■ Geological Survey of Colorado, 1869, p. 90. 



