SECT. 3] ORGANIC TRANSPORTATION OF MARINE SEDIMENTS 779 



(Shiimway, 1953). In addition to rafting rocks, kelp also transports shells, 

 foraminiferal tests and other organic remains far from the environment in 

 which they had hved. Since representatives of nearly every phylum are known 

 to live in or on holdfasts, their transportation to deep water can raise problems 

 in ecology and paleoecology. 



Smaller algae such as sea lettuce {IJlva) and some brown algae {Lessoniopsis 

 and Laminaria) have no floats but provide a sail-like surface which permits 

 somewhat stronger than normal waves and currents to move attached pebbles 

 and shells. Examples of transportation of 2-cm pebbles and shells several kilo- 

 meters were reported by Brown (1911), the movement leaving trails along the 

 bottom. 



The kelps at present have an antipodal distribution (Fig. 2), being confined 

 to cool waters of high latitudes or areas of strong upwelling (McGill, 1958). 

 However, in order to achieve this distribution they must have lived to some 

 extent at low latitudes during the colder glacial epochs of the Pleistocene. It is 

 likely that even then the kelps were more abundant at high latitudes than at 

 low ones. Because the plants can drift freely only a limited time owing to losses 

 of floats by decomposition and eating by fishes, kelp-rafted rocks and organic 

 remains are probably confined to an area within a few hundred kilometers from 

 shore: farther in cold water at high latitudes than in warm water nearer the 

 equator (Fig. 2). Rafting by kelp has probably also occurred during the geo- 

 logical past because brown algae are well known from the Miocene (Gardner, 

 1923; Emery, 1960, pp. 162-166) and lived much earlier, even in Silurian and 

 Devonian times (Krausel and Weyland, 1930). 



Locally, sand and shells are entangled and transported a short distance 

 (usually less than 100 m) in the balls of eel grass, Phylospadix, and of Posidonia 

 (Aleem, 1955) and of other plants (Olson, 1957) which are roUed onto beaches 

 from depths of a few meters, sometimes in enormous numbers. According to 

 Guilcher (1958, p. 32), Posidonia may cause a rise in the sea floor near such 

 beaches amounting to one meter per century by trapping of sediment particles 

 in the balls. Examples of algal balls, possibly of this origin, with enclosed sand 

 are reported from rocks as old as Silurian (Croneis and Grubbs, 1939). 



3. Driftwood 



Trees which grow in rocky soil commonly enclose masses of earth, pebbles, 

 cobbles and even boulders in and between their roots. These trees are sometimes 

 undermined by streams and are washed out to sea or they fall directly into the 

 sea by cliff" erosion. Once afloat they have been known to be carried thousands of 

 kilometers by ocean currents (Brooks, 1875; Rouch, 1954; Barber, Dadswell 

 and Ingle, 1959). One floating tree is reported to have held a boulder three or 

 four meters in diameter (Emery, 1955). Eventually, the wood loses its buoyancy 

 by attacks of wood-boring animals and by soaking up water so that it sinks to 

 the bottom carrying its cargo of rocks. Other logs drift ashore onto the mainland 

 or islands. Especially on the islands of the central Pacific Ocean the rocks 



