94 Couthouy on Coral Formations 



Scattered along the plateau are fragments of greatly vary- 

 ing size, thrown up by the surf, some loose, and affording 

 shelter to a multitude of small fish, Crustacea, &c. ; others 

 forming tabular masses of such magnitude as to render it al- 

 most incredible that any wave could be sufficiently powerful 

 to tear them off and transport them to their present locality. 

 They constitute one of the most remarkable features of the 

 surface reef at several islands. I have seen it for miles lined 

 with these nuclei of future ridges, from a yard square, to thirty 

 or forty feet long by four or five broad, and averaging three 

 and a half in height. Their lower portion is worn by the 

 water so as to cause the smaller blocks to assume a variety of 

 fantastic shapes. By the percolation and infiltration of water 

 charged with carbonate of lime, these masses are in general 

 firmly cemented to the subjacent coral, and converted into a 

 very solid limestone, called by seamen, '' reef-rock," in which 

 the original cellular structure is sometimes almost obliterated. 

 This reef-rock appeared to be the basis of the elevated belt 

 between the lagoon and sea, in almost every Paumotu that I 

 examined. T shall refer to these erratic blocks again, under 

 the head of re-elevation. 



It sometimes occurs that the plateau or surface reef, instead 

 of extending quite to the beach of coral sand, is separated 

 from it by a strip of smooth coralline limestone, apparently 

 formed by cementation of the finer detritus, dipping from 5° 

 to 7^ seaward, and from ten to fifty or sixty yards wide. A 

 peculiar character in these belts, is the fissures, which from 

 one-eighth to three-fourths of an inch wide, run nearly paral- 

 lel with the beach for one hundred rods together, and some- 

 times cross them at very large angles with it. There are 

 similar formations along the North coast of Tutuila, one of the 

 Samoan Group, and in its harbor, Pangopango. They also 

 occur, but of coarser texture, on the East coast of Kauai, near 

 Wailua, where they are from eight inches to two feet in 

 thickness, and are frequently quarried for building materials, 

 such as foundations, door-stones, &c. 



To this limestone shelf, or the surface reef, as the case may 

 be, succeeds a naiTOw and rather steep coral sand beach, be- 



