MR. GUPPTS EVIDENCE. 85 



" I. Thai foundations have been prepared for barrier reefs and atolls by the disintegration of volcanic islands, and by 

 the building up of submarine volcanoes, and by the deposition on their summits of organic and other sediments. 



" 2. That the chief food of the corals consists of the abundant pelagic life of the tropical regions, and the extensive 

 solvent action of sea water is shown by the removal of the carbonate of lime shells of these surface organisms from the 

 greater depths of the ocean. 



" 3. That when coral plantations build up from submarine banks they assume an atoll form, owing to the more 

 abundant supply of food to the outer margins, and the removal of dead coral-rock from the interior portions by currents 

 and the action of the carbonic acid dissolved in the water. 



"4. That barrier reefs have built out from the shore on a foundation of volcanic debris, or on a talus of coral-blocks, 

 coral sediment, and pelagic shells, and the lagoon-channel is formed in the same way as a lagoon. 



" 5. That it is not necessary to call in subsidence to explain any of the characteristic features of barrier reefs or atolls, 

 and that all their features would exist alike in areas of slow elevation, of rest, or of slow subsidence." 



The next instalment of evidence, following that of Dr. IVIurray, evidence which gives the last- 

 named authority's new theory substantial support, is contributed by Mr. H. B. Guppy with re- 

 lation to the coral formations of the Solomon Islands. This area, having been the scene within 

 post-Tertiary times of volcanic upheaval, estimated at not less than 1 2,000 feet, has revealed at 

 the hands of Mr. Guppy some important testimony concerning the thickness of the upheaved 

 coral-reefs, and the nature of their formation. Mr. Guppy's original report on the coral-reefs of 

 this region appears in the "Proceedings of the Royal Society of Edinburgh" for the years 

 1885-6, while the geological bearings are more exhaustively dealt with in a special volume, "The 

 Solomon Islands : Their Geology," &c., published in the year 1887. The analysis of Mr. Guppy's 

 evidence, embodied in Professor Bonny's appendix to the third edition of Mr. Darwin's "Struc- 

 ture and Distribution of Coral-Reefs," is freely quoted. — 



" Mr. Guppy describes the Solomon Archipelago, which includes seven or eight large islands, some being from seventy 

 to eighty miles in length, and the highest rising from S,ooo to 10,000 feet above the sea, with a great number of smaller 

 islands and islets, some of volcanic and others of recent calcareous formations. 



" The islands examined indicate upheaval in some cases to at least 12,000 feet. [Direct testimony to this effect 

 is yielded, in Mr. Guppy's opinion, by the fact that deep-sea deposits, which have been formed in depths probably of 

 from 1,000 to 2,000 fathoms, were found to compose the summit of Treasury Island, 1,150 feet above the sea, and apparently 

 also formed the capping investment of a portion of Choiseul Island at the still higher elevation of 1,500 feet and over.] 

 There are in the first place numerous small islands and islets, less than a hundred feet in height, which are composed 

 entirely of coral limestone. Then there are islands of larger size, which are composed in bulk of partially consolidated 

 volcanic muds, such as are at present forming around oceanic volcanic islands. Coral limestones encrust the lower slopes 

 of these islands, and do not attain a greater thickness than 1 50 feet. In the next place we have islands of similar structure, 

 but possessing in their centre some ancient volcanic peak that was once submerged. Then there are islands in which the 

 volcanic peak has become an eccentric nucleus, from which line after line of barrier reef has been advanced, overlying the 

 volcanic muds— islands in which he did not find the coral limestone of a thickness of 100 feet. Then we have the up- 

 raised atoll, such as Santa Anna, which, within the small compass of a height of 470 feet, displays the several stages of 

 its growth ; first, the originally submerged volcanic peak, then the investing soft deposit, and over all the ring of coral 

 limestone, that cannot far exceed 150 feet in thickness ; lastly, we come to the mountainous islands formed of old volcanic 



