Social Life in the Salt-JJ^ater JJ'orld 17 



very probable that some parts of the ocean floor form 

 the site of what ui some previous age were wind- 

 swept peaks or sun-kissed plains. Of our continents, 

 then, the ocean is, in truth, at once the cradle and 

 the grave. 



It is plain that the mobility of the sea is no incon- 

 siderable factor in shaping the destiny of the land. 

 This mobility, however, is manifested in another way, 

 and in one which is very vitally concerned with the 

 destiny of all life peculiar to the seashore. I here refer 

 to the phenomenon of the tides. 



Most of us know vaguely, perhaps, that the tides are 

 in some way influenced by the moon. This, in fact, 

 becomes evident to the most casual observer. For the 

 slightest acquaintance with the seashore soon reveals 

 the singularity that at the periods of new moon and 

 full moon occur the greatest variations in the rise and 

 fall of the water. In other words, at the time of these 

 two phases of the moon, w^hich Is to say, every fort- 

 night, the tides reach their highest point during the 

 flood and their lowest mark at the ebb. Thencefor- 

 ward until two weeks later, when the moon is in the 

 quarter phase, the variations daily grow less; after this 

 they gradually increase again until the time of new or 

 full moon. Novv^, if one is more than ordinarily ob- 

 servant he will have noticed further that the time of 

 high tide at any selected spot is always the same for 

 any given period of the cycle of the moon. 



It will be inferred, therefore, that the tides move 

 In some mysterious manner in response to the attraction 

 of a magnetic moon. But here Is a curious thing. We 

 know that the sun has a far greater attractive influence 



