THE OCEAN. 675 



miles distant, and to the Hawaiian Islands, 6,000 miles ; and on Ha- 

 waii it swept up the coast, temporarily deluging the village of Hilo. 

 An earthquake at Arica, and other parts of southern Peru, August 14, 

 1868, sent a wave across the Pacific, westward, to New Zealand and 

 Australia, northwestward to the Hawaiian Islands, northward to the 

 coast of Oregon ; and this was repeated in May, 1877. 



2. Effects of Oceanic Forces. 



The effects of oceanic forces are here treated under the heads of — 

 (1) Erosion ; (2) Transportation ; (3) Distribution of Material, or 

 Marine and Fluvio-marine formations. 



1. Erosion. 



Erosion by Currents. — Little erosion is done by the great oceanic 

 currents, on account of their slow rate of motion, and their distance 

 from the land. Still, the Labrador current, with its westward ten- 

 dency (p. 40), acting against the submerged border of the continent, 

 may have produced some results of this kind in past time, if not doing 

 so now. It has been supposed that the course of the steep outer slope 

 of this submerged border (p. 11) has been determined by the oceanic 

 currents ; but it is more probable that the position of the slope has 

 directed the courses of the currents. 



The tidal flow and wind-currents may produce results similar to 

 those of fresh- water streams of equal velocity. 



The ebbing tide and the under-current s act on the bottoms of inlets 

 and harbors, and especially their channels, and are an important means 

 of keeping them open to the ocean, and of modelling their forms. 



2. Erosion by Waves. — The waves bring to bear the violence of a 

 cataract upon whatever is within their reach, — a cataract that girts 

 all the continents and oceanic islands. In stormy seas, they have the 

 force of a Niagara, but with far greater effects ; for Niagara falls into 

 a watery abyss, while, in the case of the waves, the rocks are made 

 bare anew for each successive plunge. 



Much of their work is due simply to the impact of the water, the 

 •power of which is shown to be at times enormous by the facts cited on 

 page 671. The rocks encountered are usually more or less jointed, 

 and often laminated or bedded, and frequently there are alternations 

 of softer and easily removed layers ; so that the waters find or make 

 recesses, to give greater effect to the plunge. The slight rocking of 

 the immense slabs or blocks of jointed granite by the repeated blows, 

 enlarges the openings and brings them sooner or later where gravity 

 will finish the work of degradation. The Thimble Islands, of gneiss 



