Williams., POWELL, KING. 217 



along Marble, Cataract, Grand, Green, Horseshoe, and Split Mountain 

 Canons. In its upper part it is " Belle ropbon limestone," and in its 

 lower part the " Tampa sandstone." 



The lower Aubrey group consists of massive and shaly limestones 

 and sandstones 1,000 feet in thickness. 



The "Bed Wall group," which is most conspicuous in the Grand 

 Canon and those adjacent, has a thickness of 2,000 feet, and consists 

 of two distinct members, the upper part of massive saccharoid lime- 

 stones, the lower of indurated limestones, very irregularly stratified. 

 This division was also recognized in the Uinta Mountains. Below this 

 is a series of sandstones and shales, termed the " Lodore group," and 

 supposed by the author to be the equivalent in the Uinta Mountains 

 of the Tonto group in the Grand Canon. It forms the base of the Car- 

 boniferous formation, but is considered by Mr. Gilbert as probably of 

 Silurian age. The total thickness of the Carboniferous series amounts 

 to 4,460 feet. It rests upon the " Uinta group," which is not seen at 

 Cataract Canon, but is well displayed in the Uinta Mountains. This 

 formation in turn overlies uncomform ably the " Red Creek quartzites," 

 which are believed to be of Eozoic age. 



In his geological report on the Santa F6 Expedition, J. S. Newberry 

 reported Carboniferous, Permo-Carboniferous, and true Permian. 4 



The " upper and lower Magnesian limestone " of his report, seen near 



Cottonwood Creek, he correlated with C and B of the Nebraska City 



formations, as described by Marcou and Swallow. His correlation was 



substantially as follows : 



Nebraska City. Swallow. Meek & Hayden. Newberry. 



C. Upper Perm. Permian. Upper Magnesian limestone. 



% B. Lower Perm. Permo-Carb. Lower Magnesian limestone. 



^Ir. Clarence King 1 gave a preliminary account of the results of the 

 survey along the fortieth parallel in 1876. 



The area described in this paper extends from the eastern base of the 

 Rocky Mountains to the eastern boundary of California, along the 

 fortieth and forty-first parallels, and is a little over 100 miles from north 

 to south. The object of the paper is " to announce the strati graphical 

 divisions established in the field and their relation to the Paleozoic 

 subdivisions as established in New York and in the Mississippi Basin." 



In the region of the Rocky Mountains the entire Paleozoic series, 

 including Coal Measure beds and strata bearing Potsdam fossils, is 

 found within a section of from 900 to 1,200 feet thickness, the whole 

 entirely conformable and resting discordantly upon the Archean rocks. 

 Going westward the series expands from 1,000 to 32,000 feet. The 

 Rocky Mountain region represented Archean islands and shallows, 

 around and over which sediments were deposited, while to the west- 



4 Report of the Exploring Expedition from Santa Fe, New Mexico, to the junction of the Grand and 

 Green Rivers of the great Colorado of the West in 1859, under command of Capt. J. N. Macomh, 4°, 

 pp. 9-143. Map and plates. Washington. 1876. 



•King, Clarence: Paleozoic subdivisions on the 40th parallel. Am. Jour. Sci., 3d aer., vol. 11, 1876, 

 pp. 475-482. 



