148 CORAL AND ATOLLS 



Two thousand fathoms depth is found at an average of ten 

 miles from shore, though fifteen miles are passed towards Java, 

 and one hundred towards Australia, before this depth is re- 

 corded. Two thousand five hundred fathoms occur on an 

 average at fifty miles, and an average of one hundred and 

 eighty miles are passed before three thousand fathoms, or 

 ocean depths, are reached. 



Upon the actual cable lines the three thousand fathoms limit 

 is reached at very varying distances. Towards Java, the ocean 

 depth of 2950 fathoms is not met with before seventy miles 

 are passed, whilst towards Kodriguez one thousand miles of 

 the cable lie in depths less than 2910 fathoms, and the 

 actual cable never reaches a depth of three thousand fathoms. 

 Towards Australia, two hundred and fifty miles are passed, on 

 the cable route, before a depth of 2960 fathoms is reached ; 

 and four hundred and thirty before the bottom falls to 3130 

 fathoms. The greatest depth sounded towards Australia was 

 3500 fathoms, in Maclear deep, at a distance of four hundred 

 and fifty miles from the atoll ; towards Rodriguez 3300 fathoms 

 were met at two hundred and fifty miles from shore, and this 

 depth shoaled again, at another two hundred and sixty miles 

 farther on, into 1000 fathoms. Towards Java the bottom 

 falls away to 3535 fathoms, but 3000 fathoms is the average 

 depth of the trough which separates the atoll from Java. The 

 Cocos atoll is, therefore, the summit of a great roll of the 

 ocean floor which rises gradually, from the ocean depths of 3000 

 fathoms, at an average distance of something over a hundred 

 miles. 



Unfortunately, we do not know the soundings along the 

 line that connects Cocos atoll to Christmas Island, but it 

 may be that the ridge, from which that ancient atoll has been 

 hoisted to a height of a thousand feet, is continuous with the 

 ridge upon which the Cocos-Keeling group takes origin. 

 Again, we have no very definite data of the condition of the 

 ocean bottom to the north of the southern atoll, but it seems 

 certain that a submarine ridge streches for fifteen miles to 

 Keeling atollon ; and it is said that this ridge is nowhere 



