38 Coelenterata. 



whole atoll) since the formation of the ancient Heliopora- and Porifes-reef 

 which is found there. According to David & Sweet the surface geological 

 evidence indicates that several oscillatory vertical movements of the shore have 

 taken place in the immediate past at Funafuti. There has been a recent 

 downward movement of the shore-line to the extent of at least 6 and almost 

 certainly of 10-16 feet. Prior to this movement (which is probably still in 

 progress) there was a slight similar movement exposing the Heliopora- and 

 Ponfes-reefs to the full denuding force of the waves, followed by a contrary 

 movement of fully 8 feet, this latter motion being required to account for the 

 fact that the disintegrated coral fragments became firmly cemented in situ 

 by Lithothamnion. The general shape of the original foundation of the atoll 

 of F. has been determined by some cause, probably volcanic action or folding 

 of the earth's crust, independent of the direction of the prevailing winds and 

 ocean currents. Since its broad outlines were determined the shape of the 

 island has been modified by growth of the reef-forming plants (notably Hali- 

 meda and Lithothamnion) and animals (Foraminifera and Corals), prevalent 

 winds and ocean and tidal currents. The lowest visible foundation rock of 

 the reef platform of the atoll is Hel. with occasional Porites. Finckh states 

 that the corals are being slowly "smothered" by the abundant Lithothamnion 

 and transformed by filling-in of the interstices (with foraminiferal and other 

 sands) into the typical coral rock of the reef platform. The leeward rim of 

 the atoll is characterised by (1) the enormous quantity of branching vividly 

 coloured Lith., (2) the great abundance of Madrepora loripes (but this and all 

 other corals present are small in size), (3) the even and almost level non- 

 zonate surface of the platform and the scarcity of channels. The windward 

 rim shows (1) an absence of the branching and knobby forms of Lith., the 

 form present here being lichenous and dark-coloured, (2) a scarcity of corals, 

 Pooillopora only being found, (3) the platform is divided into erosion-, corro- 

 sion-, seaweed- and Lith.-zones and there are many extensive channels. Grouped 

 according to their importance the chief reef-forming organisms are Lith., Hal., 

 Foraminifera and Corals. The order of frequency of the corals is Heliopora, 

 Millepora alcicornis and complanata, Porites limosa, Mad. loripes and several 

 species of Pocillopora. Experiments were made on the rate of growth of cal- 

 careous algse and corals. A mass of Por. showed an increase in weight equi- 

 valent to 47 % per annum, in Hydnophora growth to the extent of 1 inch 

 in 39 months was indicated, in Poc. 1 inch in 15,5 weeks, in Montipora 

 1 inch in 35,7 weeks and in Mill. 1 inch in 34,7 weeks. - David, Halli- 

 gan & Finckh state that Madr. ceases to live at Funafuti below 20 fms. and 

 reef-building corals do not, as a rule, live below 35 fms., at which depth 

 Seriatopora is frequent. Most of the corals are limited to the zone extending 

 from low water to 10 fms. Although Hel. forms such extensive living masses 

 in the lagoon, no living specimens were obtained in dredging between 20 and 

 200 fms. According to Judd the materials from the main boring at Funa- 

 futi, which was carried to a depth of 1114V2 feet, show that the part played 

 by corals in the building up of the rock was not so great as might have been 

 expected. The corals are as often in situ in the lower as in the upper parts 

 of the core. The spaces around the entire and broken corals are filled in 

 with a detritus composed of Foramiuifera , fronds of Hal. etc., and in many 

 parts Foraminifera constitute the bulk of the rock. Much of the cementing 

 material consists of Lith. No stratification of the core was observed. In the 

 whole depth bored the same genera and species take their part in the building 

 up of the mass; sometimes calcareous algse, sometimes Foraminifera, sometimes 



