SECT. 2] 



SUBMARINE CANYONS 



491 



resembles those of west Corsica. At Triiicomalee (the former British naval base) 

 a branching rock-walled canyon comes into the bay and extends its arms so 

 close to the shore that it appears to be a truly drowned valley (Fig. 11). One 

 branch cuts directly across quartzite ridges and the walls of this gorge have 

 been visited by aqualungers who reported to the writer that there are pre- 

 cipitous rocky slopes. The outer end of the canyon has not been surveyed but 

 it definitely extends to 870 fm (1600 m) where it has walls rising 600 fm ( 1 100 m) 



Fig. 11. Trincomalee Submarine Canyon. Showing the treUis drainage pattern and the 

 crossing of the Pre-Cambrian quartzite ridges by the tributary at the head of the 

 canyon. Outer portion of canyon has not been sounded. Contour interval 100 fm, 

 with 20 fm contour added. 



or more above the floor. The right-angled bends along the canyon are indicative 

 of a trellis drainage system. 



Coming into the curving entrance to Tokyo Bay is another canyon which has 

 the steep rocky walls, the V-shaped floor, and the dendritic tributaries charac- 

 teristic of land canyons (Shepard, 1948, fig. 74). It contrasts considerably with 

 the fault-trough valleys found in the vicinity. Like many other submarine 

 canyons its wall heights are measured in thousands of feet. It terminates 

 seaward where it enters the Sagami Bay fault trough at 770 fm (1400 m). Some 

 of the tributaries come into land embayments, but unlike the Corsican sub- 

 marine canyons the main head terminates in broad shallow Tokyo Bay. 



