BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 8, pp. 87-112, pls. 10-13 February 13, 1897 



SHEETFLOOD EROSION 



BY W J MCGEE 



{Presented before the Society August 22, 1896) 

 CONTENTS 



Page 



Definitions 87 



Sheetflood work in the Sonoran district 88 



Features of the district 88 



Location 88 



Climate 89 



Topography 90 



Geology 92 



Hydrography 93 



Geologic development 95 



Stream erosion in the district , 96 



Character of streams 96 



Sources of streams 97 



Stream ways and stream-work 98 



Sheetflooding in the district 99 



Character of sheetfloods 99 



Conditions requisite for sheetflooding 105 



Erosive work of sheetfloods 107 



Sheetflood work in other districts 110 



Explanation of plates '. Ill 



Definitions. 



Commonly, running water gathers into streams and corrades channels ; 

 exceptionally, running water spreads into sheets of limited or unlimited 

 width, and, by a combination of erosion and deposition, produces plains. 



Pure water flowing over a smooth indestructible surface does not move 

 as a uniform film : if the surface is broad the sheet differentiates into 

 parallel streams of greater depth and relatively rapid flow, separated by 

 shallower bands of relatively sluggish flow ; and at the same time both 

 streams and intervening bands differentiate into series of transverse waves 

 which move forward more rapidly than the body of the differentiated 

 sheet. The tendency of flowing water to divide into streams is well 



XIII— Bull. Geol. Soc. Am., Vol. 8, 1896 (87) 



