F-26 



ported the presence of cataracts and submarine "splash pools" 

 along the thalweg axis. 



The funneling process is believed to be the one respon- 

 sible for the post-dendritic axial downcutting. Our sled 

 photography, and especially the sled pinger profiles, show 

 the lower reaches of the side tributaries often to be trun- 

 cated near the point that they would have debouched into the 

 central thalweg. We have submersible photographs of portions 

 of the truncated cross-sections of some tributaries showing 

 that the side streams have been abandoned as "hanging valleys" 

 in glacial terrains on land. Because the tributaries in 

 canyon mid-slope regions are draped with more than one meter 

 of mud, they attest to a recent inactivity in the dendritic 

 system. 



As discussed under Oceanographer Canyon, our observa- 

 tion and sampling of younger rocks in outcrops at greater 

 depths than older rocks is considered evidence for additional 

 previous intervals of canyon cut and fill going back into 

 the Mesozoic. Subsequent fillings have later been incised, 

 and we believe that the deepest excavation is the latest one. 



The distribution of outcrop within a canyon system is 

 temporal in nature. During the phases of canyon filling, 

 outcrops may have disappeared completely. Because certain 

 of the sessile communities have a preference for indurated 

 or partly indurated substrates, the extent of outcrop is 

 important if one wished to infer the broad regional distribu- 

 tions of the attached organisms. Our photo sled documented 



