10 



rROFESSOR W. J. SOLLAS. 



Captain Field's soundings, and communicated by Admiral Sir W. J. L. Wharton. 

 They present a close general resemblance, with some interesting peculiarities in detail. 



The 500 and 600 fathoms' contour lines follow approximately the outline of the 

 atoll, and are bayed outwards around the " nose " and " brow-ridge," in conformity 

 with the general outline of these features. The average distance of tliese contour 

 lines from the shore is slightly greater on the westward (leeward) side of the atoll 

 than on the eastward, so that the slope on the latter side is somewhat the steeper of 

 the two. 



The atoll is an isolated mountain rising very gently from a depth of 2000 fathoms ; 

 above 1000 fathoms the slope begins to increase, and between 600 and 700 fathoms 

 the average slope for three of the profiles is 22°, between 500 and 600 fathoms nearly 

 25^, between 400 and 500 fathoms it remains about the same, but this is owing to 

 the existence of a very gently inclined shelf, 350 yards in width, with a dip of only 

 9° or 10°, which occurs between 400 and 450 fathoms in the profile of the west side (D). 

 If this be excluded, the average slope becomes 28° to 29°, and there is a steep cliff on 

 the north profile (C) with a slope of 48° ; this cliff is interesting, since it occurs lower 

 on the flanks of the atoll than any other. Its base is 2820 feet below the sea-level, 

 and it rises through a vertical heiglit of 330 feet. The sounding ap})aratus indicated 

 coral bottom at the foot of the cliff. From 400 fathoms upwards a distinction is still 

 maintained between the southern profile and the three others, which, however, are in 

 close agreement between themselves. They present an average slojie of nearly 40°, 

 which is interrupted by precipitous and lofty cliffs, the least steep having an angle of 

 65°, the steepest, which is 300 feet in height, of 78°. The southern profile is marked 



Yiif, 4. Diagrammatic sections through the rim of Keeling (1) and Funafuti (2) Atolls. 



A. Constantly submerged portion of D. Ledge of coral-rock. J. Central flat of islet. 



the reef. 



B. Nullipore rim. 



C. Reef-flat of coral-rock. 



E. Seaward or outer ridge. L. Lagoon mound. 



r. Floor of lagoon. 



Iv. Growing reefs of lagoon. 



by a gr 



eater extension seawards of the shallow reef flat, and by an average slope of 

 only 26°, but this is greatly exceeded between 05 and 220 fathoms, the average over 

 this ranoe being nearly 40°, and it presents two steep clifl's, one of (jb°, and the other 

 of 56° to 57°, -vith a height of 270 feet. 



