692 C. R. KEYES MID-CONTINENTAL EOLATION 



gularly there is little discussion of the proofs. Among the most impor- 

 tant references are those of Newberry/ in his descriptions of the "An- 

 cient Lakes of Western America^' ; of Powell/^ in varions of his reports ; 

 of King/^ in discussing the "Geology of the Fortieth Parallel" ; of New- 

 ton/2 in his "Geology of the Black Hills'' ; of Button/^ in the "Geology 

 of the High Plateaus of Utah" ; of Cope/* in many of his detached notes, 

 and of Marsh/^ in picturing the probable environment of the "Dino- 

 cerata." In the Correlation Papers summing up general opinion regard- 

 ing American terranes, both Clark^^ and Dall and Harris^'^ accept without 

 question the lake theory. Among the most recent references to the sub- 

 ject Barbour^^ and Darton^^ hold unreservedly to the lacustrine origin of 

 the terranes. 



The present plains surface, according to the lacustrine hypothesis, is 

 merely the even lake bottom after the withdrawal of the waters. 



STREAM PLANATION 



Of late years, since it has become the custom to ascribe all plains effects 

 to the general leveling tendency of river action, most writers on the Great 

 Plains region have, without referring to the earlier lacustrine hypothesis, 

 regarded its dominant relief feature as due directly to this process. 

 Among text-books on geology Gilbert and Brigham,^° for example, state 

 that "the greater part of the vast area is a worn-down plain ; rocks which 

 were formed by the sea or by lakes have been exposed for ages to the 

 action of swinging rivers and have been pared away until the grade is 

 even from the mountains at the west to the central lowlands." 



In his recent notes on the Great Plains, Johnson^^ ascribes to them a 

 complex origin. The Tertiary and Quaternary substructure he regards 

 as alluvial when the climate was more widely arid than now. The present 

 surface relief of the central belt, or High Plains area, is called a remnant 

 of the original stream-built surface or an upland of survival. To the 

 eastward, where the country is irregularly undulating, it is regarded as 



s Fourth Ann. Kept. U. S. Geological Survey of the Territories, 1871, p. 333. 



10 Colorado River of the West, 1875, p. 150 ; also Geology of the Uinta Mountains, 

 1876, p. 163. 



11 Geological Survey of the Fortieth Parallel, vol. i, 1878, p. 457. 



12 Geology of the Black Hills, 1880, p. 188. 



13 Geology of the High Plateaus of Utah, 1880, p. 158. 

 " American Naturalist, vol. xvi, 1882, p. 177. 



15 Monograph U. S. Geological Survey, vol. x, 1886, p. 6. 



16 Bull. 83, U. S. Geological Survey, 1891, p. 111. 



17 Bull. 84, U. S. Geological Survey, 1892, p. 175. 



18 Bull. Geol. Soc. America, vol. 8, 1897, p. 307. 



18 Nineteenth Ann. Kept. U. S. Geological Survey, 1899, pt. iv, p. 719. 



20 Introduction to Physical Geography, 1902, p. 164. 



31 Twenty-second Ann. Rept. U. S. Geological Survey, 1902, pt. iv, p. 687. 



