I4O THE FLOOR OF THE OCEAN 



the submarine stream represents the concentration of silty 

 water along initial depressions with axes across the continental 

 slope and along channels dug along those lines. 



Fourth: Each subaerial stream preserves its individuality to 

 receiving basin, whether this be lake, ocean, or desert sink. 

 Our hypothesis assumes preservation of the individuality of 

 each submarine silt current on the way out to the receiving 

 basin — that occupied by the deep ocean. 



Fifth: The velocity and erosive power of the subaerial 

 stream grows with increase of gradient and with increase of 

 the depth of water, either by lateral inflow or by deepening of 

 the channel. We are to learn that similar laws must have been 

 obeyed by the silty currents. 



Sixth: The subaerial stream becomes turbulent, and there- 

 fore a more efficient excavator, when the velocity of flow sur- 

 passes a critical value. Again both theory and experiment show 

 similarity with the silty currents of the sea bottom. 



Seventh: The effective density of the running, subaerial 

 water and its eroding power are somewhat increased by the 

 addition of a load of silt, taken into suspension during the 

 erosive attack on the valley sides. Experiments have proved 

 that the same principle applied in the case of silty currents at 

 the floor of a body of cleaner water. 



Eighth: Each subaerial gully tends to become well graded 

 from end to end; any side stream generally enters the main 

 stream "at grade," that is, with no systematic break of gradient 

 at the junction. The maps of Veatch and Smith demonstrate 

 a similar condition ruling the "drainage" pattern of the conti- 

 nental slope. 



Ninth: The deepening of the subaerial gully is not contin- 

 uous, but is locally interrupted by temporary deposition of 

 sediment, fallen from the sides of the gully to the floor. The 

 channeling process has a kind of rhythm, being alternately 



