to investigate the Structure of a Coral Reef by Boring. 509 



Depth 200300 fathoms every 60 yards. 

 300400 70 



400500 ., 80 ;, 



500600 90 



., 600700 100 



700800 200 



The profiles obtained by the four series are closely similar, and, as 

 regards one important feature, almost identical. This is the sudden 

 change in slope that occurs at or about 140 fathoms. Speaking 

 generally, one may describe Funafuti as the summit of a submerged 

 conical mountain, the base of which, at a depth of 2,000 fathoms, is 

 a regular ellipse, 30 miles long by 28 miles broad. It rises with a 

 very gentle slope, which gradually grows steeper as it ascends, till 

 from 400 to 140 fathoms it has an angle of 30 ; at 140 fathoms an 



Section D. 



;,<too 



200 



to 







40 



60 

 60 

 '00 



zoo 



5OO 



575? 



too 



Two profiles of the ocean face of Funafuti. Vertical and horizontal scales 

 identical. Figures on the vertical co-ordinate refer to fathoms, on the horizontal 

 to yards. 



The curve on the left is supposed to commence 200 yards to the left of the zero 

 point. 



abrupt change occurs, and the slope becomes precipitous, making an 

 angle of from 75 to 80 for the greater part of its course, till it 

 passes into the shallow flats of the growing reef. It is difficult to 

 resist the impression that it is the upper 140 fathoms (840 feet) 

 which represents the true coral reef. A convex curvature of the 

 profile between 166 and 261 fathoms is probably a talus, produced by 

 an accumulation of coral debris. 



