618 



REPORT OF NATIONAL MUSEUM, 1904. 



Fig. 115.— Edwin Eugene Howell. 



the Archean period until late Carboniferous. From the close of the 

 Carboniferous to the beginning of the Cretaceous a great area, includ- 

 ing the entire plateau country, was covered by the waters of an inland 

 sea entirely cut off from the main ocean. Only once did the sea regain 



a temporary sway, bringing with it a Juras- 

 sic fauna and then retreating. Throughout 

 the Cretaceous age the plateau country was 

 the scene of a shallow ocean, the shores of 

 which were ever advancing and receding. 

 Through the upraising of some remote bar- 

 rier the ocean was permanently shut out and 

 the inland sea gradually converted into 

 an immense fresh-water lake, and finally 

 drained till the whole region became ter- 

 restrial. Since the expulsion of this sea 

 the elevation of the continent which caused 

 it has continued, and the plateau country, 

 which from early Silurian to late Cretaceous 

 times was slowly sinking to an extent of 

 not less than 8,000 feet, has been bodily uplifted to its former 

 altitude. 



Gilbert called attention to the almost entire absence of Upper Silu- 

 rian and Devonian fossils in the region, and described the volcanic 

 necks or plugs as vestiges of the flues through which the eruptions 

 reached the surface, the last contents con- 

 gealing in the flue to be subsequently ex- - - 

 posed b} 7 erosion. 



A. R. Marvine, who was attached to the 

 party in 1871 as an astronomical assistant, 

 was later detailed for geological work, his 

 report on the region between Fort Whipple, 

 New Mexico, and Tucson, Arizona, occupy- 

 ing pages 191-225 of the third volume. 



E. E. Howell, as a member of the survey 

 during? 1872-73, worked throughout the first 

 season in western Utah and eastern Nevada 

 and the plateau region of central Nevada. 

 In 1873 he once more entered the plateau 

 country and continued upon it to Arizona 



and New Mexico. His report is included in pages 227-300 of the 

 same volume. 



The party to which J. J. Stevenson was attached as a geologist was 

 assigned in 1873 to work in southern Colorado, the region including 

 portions of the drainage areas of the South Platte, Arkansas, Rio 

 Grande, San Juan, Grand, and Gunnison rivers. 



Fig. 116. — John James Stevenson. 



