CONICAL FORM OF THE ATOLL 117 



The expedition had other objects in view besides 

 boring. The next in importance was the investigation 

 of the atoll by sounding. This was accomplished with 

 complete success by Captain Field. Other atolls had 

 been sounded before, but never before had an atoll been 

 sounded with such accuracy and completeness as was 

 Funafuti on this occasion. The form of the floor of the 

 lagoon was made more exactly known than that of most 

 lakes in the British Isles. The slopes of the flanks of 

 the atoll were determined in four different directions, 



FIG. 34. Submarine profile of western side of atoll, drawn to true scale. 



approximately at right angles to each other and running 

 about N., S., E., and W. A study of these enables us 

 to frame a clear picture of the general form of the atoll. 

 It is a conical mountain with an oval base situated at a 

 depth of about 2,000 fathoms, measuring 30 miles in 

 length by 28 in breadth. It rises at first with a very 

 gentle slope, but gradually grows steeper as it ascends 

 (Fig. 34), till at a depth of 400 or 500 fathoms it begins 

 to present precipitous faces, and above 130 to 140 fathoms 

 is crowned by the almost vertical cliffs of Chamisso's 



