DESCRIPTION OF REMAINS OF REPTILES AND FISHES FROM 

 THE CRETACEOUS FORMATIONS OF THE INTERIOR OF THE 

 UNITED STATES. 



The Cretaceous formation in the interior of the United States covers an 

 area reaching southerly into Texas, and extending over a large portion of the 

 eastern slope of the Rocky Mountains, northerly along the region of the 

 Upper Missouri River to its sources. Exposed to view over a great extent 

 of this area, a still larger portion underlies the vast Tertiary deposits of the 

 country. Its thickness ranges from 800 to 2,500 feet, and it consists of 

 various colored strata of indurated clays and sandstones, and indurated marls 

 and limestones. So far as known, most of them are of marine origin, and 

 contain an abundance of characteristic fossils. Some of the strata con- 

 tain remains of terrestrial plants, proving that the country in the vicinity of 

 the great Cretaceous seas was clothed with forests resembling, in the generic 

 characters of the trees, the forests of our own time. Species of sweet-gum, 

 poplar, willow, birch, beech, oak, sassafras, tulip-tree, magnolia, maple, and 

 others have been described from the fossils. With such a vegetation we 

 would expect the contemporaneous existence of some forms of mammalian 

 life, but as yet, in these as well as in other Cretaceous deposits of the world, 

 no remains of mammals have been discovered. We are*, however, still on 

 the lookout for some lacustrine or river deposit of the Cretaceous era which 

 perhaps will reveal early forms of mammals — forms which may more nearly 

 relate the mammal with the reptile than any now known to us. 



Remains of birds have been found in the Cretaceous formation of Kansas, 

 and have been described by Professor Marsh. Two genera indicated by him 

 under the names of Ichthyornis and Apatornis are the most remarkable of 

 their kind, and may be viewed as the most interesting and important paleon- 

 tological discovery yet made in the West. They have biconcave vertebrae, 

 and the jaws are furnished with teeth. Like the Archseopteryx of the Solen- 

 hofen limestone, they make the relationship of birds to reptiles much nearer 

 than appears among existing forms. 



