86 SEA AND LAND 



Vet it is likely that only a small part of these elevations 

 attain the surface of the ocean. i^robably the greater part 

 of them remain buried beneath the sea, and are onh' imper- 

 fectly perceived when the sounding lead indicates an elevation 

 of the bottom. Thus on the floor of the North Atlantic there 

 is apparently a long discontinuous chain of these elevations 

 extending from the Icelandic oroup of islands southward to 

 the Azores. If an explorer could view this part of the sea- 

 bottom he would probably find that the line of craters was as 

 continuous as that exhibited b)- the volcanoes of the Andes. 

 In the invisible landscape of the sea-floor, volcanoes play the 

 part of mountains on the land. It seems indeed clear that 

 these elevations, due to the action of the earth's interior fires, 

 are in their way as characteristic of the deeper seas as the 

 mountains are of the land portion of the continents : the 

 volcanic field is so essentially marine, that of the hundreds 

 of vents that have been in activity within the historic period 

 not one is situated more than three hundred miles from the 

 marofin of the sea. 



Besides the volcanic peaks the sea-bottom in certain parts 

 of the tropics and in the regions near to the e(|uatorial realm 

 which are swept over by warm ocean currents is beset with 

 the sin^rular elevations formed bv coral reefs. Next the 

 shore these reefs take on the form of long submerged walls, 

 sometimes many hundred miles in length and only a hundred 

 feet or so in height. To the eye they would appear as singu- 

 larly regular and artificial terraces, their crests on an exact 

 level for a considerable part of their length. Here and there 

 the wall would present port-like openings through which the 

 streams of the tides and rivers find entrance and egress. The 

 reefs of the deeper sea present a very different aspect ; they 



