150 THE FLOOR OF THE OCEAN 



turbulent soon after passing the fall-off, as illustrated by the 

 mottled appearance of the dark tongue, photographed from 

 above (again through the clear overlying water) and appear- 

 ing in Figure 78. With the onset of turbulence the current 

 began to deepen the initial depression directed down the "con- 

 tinental slope," making this into a "canyon" or "furrow." 

 With the erosion went a gain in load for the current and also 

 measurable acceleration of its velocity. Thus Kuenen proved 

 once more that "to him that hath shall be given." 



In order to make more vivid the evidence for erosion and 

 self-acceleration of current, both to the eye and to the camera, 

 clear solutions of salt in water were released on the "shelf," this 

 time covered with a thin layer of white mud. As shown in 

 Figure 79, this denser, saline water did rush down the "slope" 

 and tore up and incorporated some of the bottom mud. Note 

 that the photograph was taken looking into the side of the 

 tank; and that the lower section is a continuation of the upper 

 section. Figure 80 depicts on a somewhat larger scale the 

 turbulent mass, clouded with the new load of suspended, solid 

 matter. 



Kuenen measured the velocities of flow and was able to esti- 

 mate the average thicknesses of the moving sheets of "heavy" 

 water, as seen through the glass walls of the tank. Knowing 

 also the slope of the bottom, he had the data for applying an 

 engineer's formula, which with proper precautions can be used 

 to calculate the velocity expected for a current flowing steadily 

 down a continental slope. This formula reads: v = c^/ m.s.d, 

 where c is a constant; v represents the velocity; m, the so-called 

 hydraulic mean depth (the cross-section of the current divided 

 by its wetted perimeter) ; s, the slope down which the current 

 runs; d, the effective density of the flowing mixture of water 

 and silt. 



From the measured values of v, m, s, and d in the case of a 



