TERTIARY CONTINENTAL HYDROCLASTICS 62y 



distance from the mountains the beds consist of coarse red sand- 

 stones interbedded with clays and arenaceous marls. In the Arapa- 

 hoe and Denver formations of Colorado, basal conglomerates from 

 50 to 200 feet in thickness are succeeded by arenaceous clays, and 

 these, in turn, are followed by 400 feet of eruptive debris, above 

 which are again conglomerates and sands derived from the moun- 

 tains. Cross-bedding and wedging out of layers are common, show- 

 ing a considerable current. In some of the beds "tree stumps in 

 erect position with roots in mud layers and broken trunks in sand 

 or gravel . . ." occur (Cross-i6:jd5') and contemporaneous 

 lava flows are interbedded with the sediments. 



In these deposits the remains of terrestrial vertebrates are fre- 

 quently abundant, while fresh water animals are found only where 

 temporary bodies of water existed. Associated with typical atmo- 

 clastic are lacustrine deposits, often rich in remains of fish or 

 other fresh water animals, and eolian deposits (anemoclastics). 

 Not infrequently the atmoclastics extend out covering either lacus- 

 trine or eolian deposits. 



The Eocenic and Oligocenic deposits of the Wind River and 

 Bighorn basins in Wyoming have already been referred to. These 

 deposits consist of clays and sands often well banded and alternat- 

 ing red and bluish in color, of arkose sands, and of conglomerates 

 and occasional fine tuffs or pyrolutytes. They contain land and 

 river vertebrates, such as crocodiles, turtles, garpike, Eohippus, 

 Heptodon, Lambdotherium, etc., and shells of Unio. Microscopic 

 as well as macroscopic study of the deposits has shown that they 

 are derived from the crystalline or other rocks of the enclosing 

 mountains, and their character and mode of occurrence show that 

 they were either wind or river transported. In the coarser sand- 

 stones and arkoses of the Wind River and Bridger ( ?) beds, 

 Archsean granites and Palaeozoic quartzites are readily recognizable. 

 "The well-rounded gravels, found in some of the arkoses, point 

 with equal certainty to running water as the transporting agent, 

 while fluviatile deposition is shown by the frequent channels filled 

 with coarse sandstone which cut irregularly across the finer clays, 

 by the frequent interstratification of sandstone lenses with the clays 

 and by the presence in the latter of fish, crocodiles, and turtles, 

 and occasional beds of Unios. Local swamps are indicated by 

 lignites in the blue clays and sandstones, but never in the red 

 clays." 



Sometimes change in climate or stee|)ening of grade is indi- 

 cated by coarsening of sediments . . . "for instance, the 

 coarse, frequently cross-bedded arkose forming the lower member 



