IN THE DEPTHS 



56 



is of coral formation and rests upon a huge 

 tower of limestone somewhat like a capital 

 upon a column. The soundings off the edge 

 of the reefs give a depth of about 2,400 

 fathoms, showing that here is a mighty butte, 

 capped with coral, rising sheer through two 

 and a half miles of water to the surface. St. 

 Helena and Ascension Island, both of volcanic 

 formation, also rise abruptly from great 

 depths; and to the north of New Zealand there 

 is a submerged basin from which lift marine 

 sierras some thirty thousand feet without quite 

 breaking the water line. But generally speak- 

 ing there are few mountains in the sea other 

 than those of coralline or volcanic origin. It 

 is not probable that there are any extensive 

 ranges or that there are great wrinkles or folds 

 in the earth's crust underlying the depths. 

 This is, of course, conjecture; and yet circum- 

 stances of dredging and sounding seem to con- 

 firm it. 



The pot-holes that sink far below the average 

 depth are just as rare as the elevations that rise 

 to abrupt heights; but still they do exist in 

 certain places. Off the shores, or " conti- 

 nental benches " as they are called, there are 

 sometimes swift descents to almost fathomless 

 depths — descents as over the edge of cliffs and 



Volcanic 

 and coral- 

 line forma- 

 tions. 



Pot-holea 

 and chaama. 



