NARRATIVE OF THE EXPEDITION IN 1896. 



21 



Fig. 13. — Reproduction of a photograph of Hcliopm-a ccerulea, as seen on the floor of the Mangrove Swamp. 



than its companion, around which it forms a wide fringe (fig. 14). In many cases 

 the surface of the Porites, which has been etched by the solvent action of sea 

 water, reveals a distinct lamellar structure, running concentric with the margin. 



Fig. 14. — Diagrammatic sketch to illustrate the branching of Heliopora and its association with Porites. 



The level tops of the Porites clumps look like a series of stepping-stones, about 

 which the frayed ends of the Heliopora lamellge stand like broken reeds, 6 inches 

 above the floor of the swamp. For a great part of the day nearly the whole of the 

 floor of the swamp lies bare and dry, but it is submerged several feet at high 

 water ; the sea gaining access to it through a number of transverse fissures, which 

 are concealed from sight for the most part, but revealed as rounded pot holes in the 



