A GREAT SEA- WAVE. 



209 



minute, consists, in the deep ocean, of a long low 

 swell of enormous volume, having an equal slope 

 before and behind, and that so gentle that it might 

 pass under a ship without being noticed. But when it 

 reaches the edge of soundings, its front slope becomes 

 short and steep, while its rear slope is long and gentle.' 

 On the shores visited by such a wave, the sea would 

 appear to rise more rapidly than it sank. We have 

 seen that this happened on the shores of the Samoa 

 group, and therefore the way in which the sea rose 

 and fell on the days following the great earthquake 

 gave significant evidence of the nature of the sea- 

 bottom in the neighbourhood of these islands. As 

 the change of the great wave's figure could not have 

 been quickly communicated, we may conclude with 

 certainty that the Samoan Islands are the summits of 

 lofty mountains, whose sloping sides extend far towards 

 the east. 



This conclusion affords interesting evidence of the 

 necessity of observing even the seemingly trifling 

 details of important phenomena. 



The wave which visited the New Zealand Isles was 

 altogether different in character, affording a note- 

 worthy illustration of another remark of Mallet's. He 

 says that where the sea-bottom slopes in such a way 

 that there is water of some depth close in-shore, the 

 great wave may roll in and do little damage ; and we 

 have seen that so it happened in the case of the 

 Samoan Islands. But he adds, that ( where the shore 

 is shelving, there will be first a retreat of the water^ 



