MESOZOIC CONTINENTAL HYDROCLASTICS 633 



beginning of marine invasion, the river building processes being 

 overcome by the invading forces of the sea. (See further, 

 Barrell-6.) 



The Red Beds of North America. The Red Beds of the Rocky 

 Mountain region and the similar red sandstones of the Newark 

 formation of the eastern United States are now generally recognized 

 as subaerial deposits, in part of fluviatile and in part of eolian 

 origin, with subordinate lacustrine and rarely estuarine conditions. 

 The source of the western red beds was the old Palaeocordilleran 

 chain of mountains formed at the end of the Palaeozoic, and 

 extending northwestward from Arizona to northern California. 

 On the Pacific side of this chain marine Triassic and Jurassic beds 

 were forming, while east of the range a series of alluvial fans ac- 

 cumulated, these being now in part represented by the Red beds. 

 Their highly oxidized character indicates that accumulation was 

 under semi-arid climatic conditions, such as would prevail with a 

 westerly wind sweeping over a mountain chain of sufficient height 

 to deprive it of most of its moisture. That vegetation, neverthe- 

 less, existed in some parts of the mountain slopes is shown by 

 the abundance of the petrified woods preserved in these deposits, 

 into which they were probably carried by torrential streams. Ac- 

 cording to Williston and Case (59) the upper Red beds, from 

 Lander, Wyoming, on the north to New Mexico, Kansas, and Texas, 

 on the south, range from five hundred to possibly a thousand feet 

 in thickness and are "barren or almost barren measures character- 

 ized by light colors of the sandstone, often of eolian origin, and 

 more or less interspersed or capped with massive beds of gypsum." 

 It may be added, however, that some authors still hold to the ma- 

 rine theory of origin of these beds. (See, especially, Henning-28.) 



Vertebrate fossils of Triassic (Keuper) age are reported from 

 all along the line of outcrop, chiefly comprising phytosaurs and 

 labyrinthodonts, closely agreeing with species from the European 

 Keuper. Some of the lower Red beds of the southern and western 

 region are of Permic age, and indicate the earlier commencement 

 of this type of sedimentation. 



Triassic Red Beds of Eastern North America and of Europe. 

 The Newark series is likewise best regarded as forming local 

 remnants of a combination of widespread alluvial fans, river flood 

 plain, and eolian deposits, derived from the Appalachians to the 

 west and built out toward the east on the low coastal plain, or into 

 depressions, and under conditions of semi-aridity which permitted 

 pronounced oxidation of the sediments. The beds themselves 

 abound in shrinkage cracks, raindrop impressions and animal foot- 



