Wharton's and Darwin's theories of coral reefs.

Abstract

There is a passage in Gardiner's review (1) of my book on coral reefs (2) which puzzles me. He there wrote: be that Wharton's views ... are 'against consensus of geological opinion,' but I failed to find any cited against Wharton's idea of an island being cut down by waves and currents to a flat bank 30-40 fathoms deep. Taken with context, this can only mean that Gardiner regards Wharton's theory of atolls as still tenable; for if it be agreed that foundations of atolls actually been prepared by cutting down volcanic islands to flat submarine banks, as Wharton believed, later upgrowth of reefs around bank margins to atolls is acceptable enough. puzzling part of above quotation is therefore that Gardiner appears to have failed to find any evidence cogently cited against Wharton's theory; for, as I see case, counterevidence is not only manifest and abundant but also unquestionable and convincing. In order to make this clear, let us look somewhat closely at theory which Wharton proposed. That experienced hydrographer was impressed, some thirty-five years ago, with flatness of atoll-lagoon floors, in which he could not find deeply concave of Darwin's text (1842, 93); but Wharton there misunderstood Darwin's meaning, for, although originator of subsidence theory of coral reefs also used other similar phrases, such as saucer-shaped hollow (28) and bason-like form (92) in connection with atoll lagoons, he elsewhere stated explicitly that the greater part of bottom in most lagoons is formed of sediment; large spaces exactly same (20), thus showing that concavity is subordinate to flatness, and he very properly adduced processes of aqueous deposition to account for flatness with which lagoon-floor sediment are spread out. Wharton was also impressed with moderate depth, 30 or 40 fathoms, of many lagoons, and asked whether that restricted depth may not be general limit of power of oceanic waves to cut down mass acted upon when it is friable (Brit. Assoc. Rept., 1894, 709); but he nowhere showed that fairly friable rocks prevail in atoll foundations. Three years later he made a fuller statement of his views in an article entitled The Foundations of Coral Atolls (Nature, 1v, 1897, 390-93); and here he wrote: Toward sides of a lagoon depth gradually lessens; hence difference of opinion between Wharton and Darwin on this point would seem to been rather verbal than factual. Darwin was considering chiefly reef, and emphasised slope by which descent is made from it to flat lagoon floor; Wharton was concerned chiefly with lagoon floor, and emphasised general flatness of its surface, from which a gradual ascent is made to encircling reef. It is in Wharton's article of 1897 that some account is given of certain members of group of drowned atolls north of Fiji, for which I proposed name, Darwin Hermatopelago, or Sea of Banks. Wharton there wrote: The remarkable thing about these banks is absolute uniformity of depth of water over their areas inside low [submerged] rim of growing coral which encircles their edges in various degrees. Alexis bank is represented in a full-page figure with many soundings; its outer rim has diameters of 15 and 8 miles, with depths of from 13 to 20 fathoms; its floor measures 12 by 7 miles with depths of from 24 to 28 fathoms. Other banks are said to measure 22 by 10 and 18 by 9 miles with floors of similarly equable depths. But not enough emphasis is given to fact that, by reason of bank rims being submerged, banks are swept over by swell coming, not greatly impeded, from open ocean; or to inference that, by action of swell, exceptional smoothness of bank floors be accounted for. It is then asked: What causes this remarkable similarity of depth and this extraordinarily even surface over these large banks? …