SECT. 2] 



MICROTOPOGBAPHY 



465 



Fig. 36. 42° 53'N, 26° 45'W. Depth 3080 m. Foothills of the Mid-Atlantic Ridge. Area of 

 picture 3 by 5 m. (Photo by N.I.O.) 



Spiral and helminthoid raised tracks made by organisms burrowing just under the 

 surface. Note the spiral ending in the centre where the organism has presumably 

 burrowed straight down. 



termination of tracks (Fig. 36), the presence of wormcasts, of worms themselves 

 protruding from the bottom, and of radial feeding tracks where repeated 

 excursions of tentacles from the burrow have made marks radiating from it 

 (Fig. 37). 



A quantitative approach to these disturbances can be made in two ways, by 

 considering the surface distribution of disturbances and the effective diffusion 

 downwards of surface material. To consider the surface distribution, nearly 

 500 photographs of sediment-covered areas were examined from 28 stations in 

 the North Atlantic and in the Gulf of Mexico. The percentage area disturbed 

 by mounds, holes and tracks was estimated for each station. The results, 

 classified in terms of physiographic regions, are summarized in Table II. 



Table II 



