64 



HERSEY 



[chap. 4 



and the several seamounts to the north. The shallower layers are probably 

 sediments, but the shapes of the dee]ier retlectors together with their associa- 

 tion with the seamounts suggest a volcanic origin. At this writing there has 

 been no o})portunity to investigate these structures in any detail. Thus we can 

 only speculate about the significance of the obvious interruptions in the 

 horizontal reflectors in both profiles. Some of the interruptions on both profiles 



TRAVEL 

 -TIME 0.25 

 IN 

 SECONDS 



0.20 



0.15 



■0.10 



0.05 



REVERBERATION 



BOTTOM 



REFLECTIONS 



REFRACTED 

 ARRIVALS 



r.-'-'-y-^. 



ELECTRICAL 

 CROSS-FEED 



FROM 



POWER SUPPLY 



OF SOURCE 



— lO,25 



Jbottom 

 reflections 



15 



0.10 



0.05 



Fig. 16. A dual-channel recording of a refraction profile in Buzzards Bay, Massachusetts. 

 Channel 1, filtered 75 c/s hi -pass. 

 Channel 2, filtered 1200 c/s hi-pass. Gain of channel 1, 30 dB higher than channel 2. 



correspond through several successive reflections in depth suggesting either 

 buried seamounts or intrusives. 



Figs. 14 and 15 were recorded over the Bermuda rise. The deeper refiector 

 of Fig. 14 is characteristically rough and has large relief. This recording was 

 taken within 90 miles of Bermuda; 60 to 70 miles farther to the southwest, as 

 in Fig. 15, a similar reflector is overlain by several nearly horizontal, strong 



