574 H. B. GUPPY ON THE RECENT 



reason, the calcareous muds and sands found at the bottom of the lagoons are 

 of coral origin, representing as they do the final stages of the process of 

 degradation. The variety in character exhibited in the following groups of 

 coral limestones may be thus in a great measure explained : — 



(1) Coral rocks, properly so called, which are merely the massive reef- 



corals in different stages of fossilisation. The porous and small- 

 celled corals, as the Poritidce, are the first to lose their characteristic 

 structure, usually passing through a drusy stage, when they present 

 a saccharine appearance, and finally, by the continued percolation of 

 water charged with calcium carbonate, assuming a compact texture 

 exhibiting no coral structure to the eye. Such coral rocks are best 

 observed at the coast. 



Here I may refer to a peculiar variety of coral rock which is not 

 uncommon on the south side of Treasury Island on the higher slopes 

 of the hills, as high as 750 feet above the sea. It is a hard, compact, 

 partly crystalline greyish rock, chiefly made up of a coral belonging to 

 the Fungiclae, which Mr J. J. Qtjelch, to whom fragmentary specimens 

 were submitted for examination, has identified as being with very 

 little doubt Leptoseris striatus (Kent), a species founded for the 

 reception of a rare coral collected by Capt. Sir E. Belcher at Borneo, 

 (the only other recorded specimen being from Madagascar (?). This 

 coral is not included amongst my collection of reef-corals in the 

 Solomon Islands. It may probably, however, occur in the deeper 

 water.* 



(2) Coral rocks, which are chiefly made up of calcareous Alga3,t fragments 



of Molluscan shells, corals, and Echinoderms, the interstices being 

 filled up by the tests of Foraminifera and other small calcareous 

 organisms. In the composition of such rocks, coral fragments take 

 only a secondary part. The majority of coral limestones that I found 

 in the Solomon Islands may be referred to this division. They arc 

 usually white in colour, but often reddish or yellowish brown, being 

 hard, compact, and sometimes partly crystalline in texture, and often 

 displaying a fragmental structure. The percentage of calcium 



* In one of the islands of the Pelew Group, Professor Semper observed that the base of the coral 

 cliffs was formed entirely of species of Lophoseris mixed with other deep-sea forms, the higher portion 

 of the cliffs containing Astrceidce, Poritidce, Madreporidce, &c. Lophoseris and Leptoseris belong to the 

 same sub-family of the Fungidw. See The Natural Conditions of Existence, &c., p. 275, London, 1881. 

 I am inclined to consider this variety of rock in Treasury Island as representing the base of the elevated 

 reef-masses, since it only occurs on the higher and more denuded slopes. 



t Some specimens of coral rock which I obtained at Santa Anna were entirely formed of the joints 

 of a calcareous Alga, resembling apparently the genus Halimcda, which are found commonly in the sound- 

 ings off the outer edge of the present coral reefs. 



