P A K T I. 



THE CLASSIFICATION AND DISTRIBUTION OF THE CRETA- 

 CEOUS DEPOSITS. 



Messrs. Meek and Haydeu have classified the vast thickness of the Cre- 

 taceous formations of the West from observation of the section made by the 

 Missouri River from near its sources to the point where it enters the Carbon- 

 iferous strata of Eastern Kansas. This classification has been found by Dr. 

 Hayden to be applicable to the exposures of the rocks of this period along 

 the eastern base of the Rocky Mountains ; and I may add that an examina- 

 tion of the western flank of the same mountain-region in New Mexico, con- 

 ducted by myself, under direction of Lieut. Gr. M. Wheeler, United States 

 Engineers/ has extended the application of the same system. 



The classification of Messrs. Meek and Hayden embraces five distinct 

 ejjochs, all of marine deposits. The lowest is a sandstone, which rests uncon- 

 tbrmably on Azoic, Carboniferous, Jurassic, or other beds, as the case may 

 be : it is succeeded by a series of usually dark-colored shales or clays, or 

 No. 2, which is overlaid by a gray, white, or yellow chalk or calcareous marl, 

 which forms the surface-rock of^a large area; this is No. 3. The superincum- 

 bent divisions, Nos. 4 and 5, consist of laminated shaly clays and sandy beds 

 respectively. Above this point, the character of the deposits becomes brackish 

 and lacustrine, constituting an approximation to the overlying Tertiary forma- 

 tions. This physical change has been regarded by the stratigraphers as tlie 

 boundary-line between the Cretaceous and Tertiary periods; and (he indica- 

 tions derived from the vegetable fossils are not inconsistent with such a view. 

 The vertebrate paleontology, on the other hand, shows the interruption in that 

 kind of animal life to have taken place much higher up in the series; hence, 

 in the present work, the Lignite, or Fort Union, epoch is included in the 

 Cretaceous formations as No. 6. 



'See Appendix F F 3 of Anuual Kepoit of the Chief of Engineers, Wasbington, 1874. 



