PERMANENCE OF OCEANS 8 1 



the water. The emerged mountain-tops often form a fringe 

 of islands extendinof some distance from the coast-line, and 

 the valleys are prolonged as deep bays which penetrate far 

 into the land. Thus the land and the sea appear to be 

 blended in a way that very naturally leads to the supposition 

 that the ocean-t^oor is merely an inundated portion of its 

 surface, differing from the dry parts only in the absence of 

 certain minor features, such as river-valleys which are due to 

 actions peculiar to the land. 



Naturalists for a long time adopted this popular view 

 concernincr the conditions of the sea-bottom. Observing that 

 the greater part, if not the whole, of the land was made up of 

 sediments which had been accumulated on the sea-floor, the stu- 

 dents of this field were led to the idea that sea and land had 

 often changed places ; no part of the earth for any long period 

 escaping from the invasions of the ocean. Gradually, with 

 the advances in knowledge concerning the history of the 

 earth, these students have been driven to other views. While 

 they are thus forced to allow that the continents have been 

 subjected to great alterations of form, a part of their surface 

 from time to time sinking beneath the sea while other 

 portions which had long been under water rose above its 

 surface, they find good evidence that, as a whole, the seas and 

 lands have not changed places, but that the greater oceans 

 have been permanent features in the physiography of this 

 planet. There is doubtless a debatable area .next the shores 

 of each continent, which is now won to the realm of the land 

 and now to the domain of the waters, but there remains a 

 vast field, probably including more than half the oceanic area, 

 which for a great time, perhaps since organic life has tenanted 

 this sphere, has been always in the condition of deep sea. 



