658 B DYNAMICAL GEOLOGY. 



Sea-weeds are borne on by the Gulf Stream in great quantities, 

 and thrown off on the inner side of the current into the great area 

 of still water about the centre of the North Atlantic, called, from 

 the common name of the plant (a species of Fucus), the Sargasso 

 Sea. With the sea-weeds, there is a profusion of small life, — fishes, 

 crabs, shrimps, Bryozoans, etc. 



Pourtales, in microscopic examinations of soundings from beneath the Gulf 

 Stream, found an abundance of the shells of Rhizopods, and almost no proper 

 detritus. Bailey suggested that these minute cellular shells were drifted to their 

 pla:e by the stream; but Pourtales concludes, from his observations, that they 

 live at the depths in which they are found. 



In polar seas, where there are glaciers and icebergs, large quan- 

 tities of gravel, earth, and boulders are often floated off on the 

 bergs. From the Arctic they are borne south by the polar current 

 to the Banks of Newfoundland ; there the icebergs encounter the 

 edge of the Gulf Stream, and melt, dropping their freight over the 

 bottom. 



Tidal and wind currents have the same powers of transportation as 

 rivers of equal velocity. 



2. Transportation by waves. — As follows from the force of waves 

 against shores, stated on p. 654, they have great transporting 

 power ; but their action is confined to narrow limits of depth, and 

 is exerted mainly when the plunging waters strike and dash upon 

 a sandy or rocky coast. Large rocks often have their buoyancy 

 increased by the sea-weeds attached to them. 



Stevenson reports that a block of gneiss of 504 cubic feet (about forty -two 

 tons) lying on a beach (in Scotland) was moved five feet by the waves during 

 one storm, and was then so wedged in that its farther progress was prevented. 

 The in-coming wave, as it struck it, gave it a shove, and, pushing on, buried it 

 from sight, making a perpendicular rise of thirty-nine or forty feet ; and in the 

 back run the mass was again uplifted with a jerk. 



Marine animals, or their relics, and sea-weeds, are thrown abun- 

 dantly on coasts by the waves ; and, in some regions, whales that 

 venture too near the land are carried up and left floundering on 

 the sand. This happens not unfrequently about the Chusan Islands 

 in the China Seas, where the tidal currents have great force (p. 

 653). 



In the case of the heaviest waves, and especially earthquake- 

 waves, the waters first retreat to an unwonted distance, and then 

 advance in their might, striking deep, and tearing up strata that at 

 other times are under the protection of the waters. 



In the wave-movement on soundings, and not close in-shore, the 

 propulsion of each wave is very small ; and its power of accomplish- 



