Table 1. Surface-sediment echo character and their interpretation. 



Echo character 



Sediment interpretation 



Letter 

 designation 



Very poor multiple,^ smooth surface. 



Soft, nearly fluid mud 



M 



mostly transparent, may have conti- 







nuous, multiple, parallel internal 







reflectors. 







Very poor to poor multiples. 



Sandy mud 



X 



slightly irregular surface (rougher 







than M) , nontransparent (a noisy 







record) . 







Good multiples (commonly two to 



Muddy sand 







three) , smooth to slightly 







irregular surface (similar to X) , 







nontransparent . 







Fair multiples,^ hummocky to gently 



Sand 



S 



rolling but smooth surface, 







commonly nontransparent. 







Poor to good multiples (mostly fair). 



Clay and clay with gravel 



T 



smooth or irregular surface (in 



(probably till) 





between S and R) , commonly irregu- 







lar internal reflectors. 







Fair to good multiples (commonly 



Rock (probably shale) 



R 



three or more), commonly a broken. 







irregular surface (may look similar 







to T) , and may have closely spaced 







discontinuous, internal reflectors. 







Fair to good multiples and a 



Rock waste (shale derived 



RW 



jagged, irregular surface. 



from a harbor excavation) 





Very poor multiple: a discontinuous multiple if present. 



Poor multiples: one to two multiples; the first multiple is commonly 

 discontinuous . 



Fair multiples: one to two multiples; the first multiple is commonly 

 continuous . 



Good multiples: two to seven multiples; the first and second multiples 

 are commonly continuous. 



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