Page:Proceedings of the Royal Society of London Vol 60.djvu/545

Rh Depth 200—300 fathoms every 60 yards. „ 300—400 „ 400—500 „ 500—600 600—700 „ 700—800 11 70 „ 80 .. 11 1 1 b0 „ 100 „ 9? 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.

Two profiles of the ocean face of Funafuti. Yertical 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.