874 



HISTORICAL GEOLOGY. 



Neocomian or Lower Cretaceous ; besides, at least one species of shell 

 occurs in both regions. It is thus shown that the belt still existed during 

 the early Cretaceous, and that, at the same time, as he observes, some 

 barrier along the region separated in India an eastern zoological province 

 from a western. With reference to the connection of South Africa with 

 Australia, all known facts would be explained if it were confined to the 

 Permian and early Triassic periods. 



POST-MESOZOIC REVOLUTION: MOUNTAIN-MAKING AND ITS 



RESULTS. 



The upturning. — The close of Mesozoic time was marked by the making 

 of the greatest of North American mountain systems. The upturnings took 

 place along the summit region of the Eocky Mountains, where over a broad 

 belt, as long probably as the western side of the continent, a series of 

 geosynclines had been accumulating deposits ever since Archaean time. 

 This mountain system of North America, which stands as the Mesozoic 

 time boundary, is the Laramide system already described, explained, and 

 illustrated on pages 359-364. The system includes the Wasatch range, 

 and others to the north and south. Another figure (Fig. 1467), representing 

 a section of the Lower Cretaceous in the eastern mountain range of Mexico, 

 northwest of Monterey, is here added from a paper by R. T. Hill. The 

 beds stand in a series of nearly vertical anticlines and synclines, from 



1467. 



Section showing the folding of the Comanche limestone In the eastern mountain range northwest of Monterey. 



K. T. HiU. 



participation in the system of Laramide upturnings. A section showing 

 vertical beds of limestone and a flexure in the Chinate Mountains, 25 miles 

 north of Presidio, not far from the boundary of Texas, is published by 

 C. A. White in his Correlation Report on the Cretaceous of North America. 

 Further, Streeruwitz has given sections illustrating the upturned condition 

 of the Cretaceous formation of the Sierra Blanca and other mountains in 

 Trans-Pecos, or western, Texas. 



The great belt of orogenic work extending from the Arctic regions 

 through North America, was probably paralleled by like work, of equal 

 extent, in South America, but on a more eastern line. A long lesson with 

 regard to the comprehensiveness of mountain-making forces and work is 

 afforded by the single case of North America ; and it comes with tenfold 

 emphasis if the western borders of the two Americas, through 120° of 



