778 



EMERY 



[CHAP. 28 



observed several hundred kilometers from shore in waters several kilometers 

 deep. In fact, free-floating kelp was taken as one of the signs of nearness to the 

 rugged California coast by pilots of the Manila galleons en route to Acapulco; 

 thereupon, the galleons were turned to a southeasterly course to reach Acapulco 

 (Schurz, 1959, p. 239). An unknown percentage of these freely drifting kelps 

 still tow their rocky anchors through the water. An example reported by Menard 



Fig. 2. Areas of greatest importance to chief transporting agents of coarse sediments. 



Kelp: cross-hatching shows areas likely to be reached by kelp rafting from coastal 

 zones where kelp lives. (After McGill, 1958.) 



Sea mammals: cross-hatching shows areas where transportation by sea-lions and 

 most other sea mammals may occvir. (After Scheffer, 1958.) 



Ice: dashed line indicates equatorward limit of present-day floating ice; cross- 

 hatching shows areas where bottom sediment may be classed as glacial-marine 

 origin. (From Dietrich and Kalle, 1957; Hough, 1956; Menard, 1953; and others.) 



Turbidity currents: cross-hatching shows areas accessible to turbidity currents, i.e. 

 omits mid-oceanic ridges, continental shelves. (Modified from Elmendorf and Heezen, 

 1957.) 



(1953) was a raft of Nereocystis about 500 km offshore in the Gulf of Alaska 

 suspending a subround pebble about 8 cm in diameter. At least two rocks 

 having remnants of holdfasts were dredged from the bottom at depths of about 

 215 m off southern California, but many other rocks have been similarly rafted 

 and their holdfasts decomposed or eaten by benthic animals. Rounded and 

 partly pholad-bored pebbles and cobbles of various rock types dredged from 

 about 3800 m off western Mexico have thus been attributed to kelp rafting 



