F-11 

 Their overall thalweg gradients exceed 3° (Fig. F4) . Back- 

 tilted terraces are much more limited than at Baltimore 

 Canyon, and are confined to the canyon head areas (Fig. F3, 

 F5) . The floor of the thalwegs of Oceanographer and 

 Lydonia Canyons are seldom more than 50 m in width, whereas 

 Baltimore commonly exceeds 400 m. As in Baltimore Canyon, 

 Oceanographer and Lydonia Canyons have numerous lateral 

 second and third order tributaries, in most instances origi- 

 nating below the shelf edge at depths generally greater than 

 200 m. The heads of the tributaries are shallowest in Ly- 

 donia Canyon. 



In Oceanographer and Lydonia Canyons, axial downcutting 

 seems to be still active, and the floor of the thalweg is 

 littered with numerous talus blocks (Trxombull and McCamis, 

 1967, Ryan et al . , 1978), recently avalanched from the out- 

 crop belts. Here, outcrops extend almost always right down 

 to the edge of the thalweg floor. In our field program, we 

 sampled these outcrops (Tables F2, F3) , finding good agree- 

 ment with the fossil ages determined by pervious samplings 

 by Stetson (1936, 1949) and Gibson et al. (1968) . 



The Cretaceous age at most of the Oceanographer Canyon 

 axial outcrops suggests that these indurated strata are bed- 

 rock exposures rather than downdropped allochthonous units 

 of the canyon wall. Upper Turonian (95 m.y.B.P.) outcrops 

 in Oceanographer Canyon occur at depths below 950 m and in 

 Lydonia Canyon below 600 m. We also sampled indurated sedi- 

 ments belonging to Coniacian, Santonian, Campanian, and 



