1909.] ON SKULLS OF SOUTH-AFRICAN FOSSIL REPTILES. 679 



form. In the middle o£ the interval between two islands the 

 inrushing current sweeps on farthest, and its burden of sand is 

 dropped in the lagoon oi:>posite the gap in the island ring. 



This process accounts for the existence of those atolls that have 

 the most land upon their leewa,rd side, and an entrance guarded hy 

 a hreccia platform upon their windwju-d side. The sand swept in 

 at tlieir windward side is deposited upon the lee side of the lagoon 

 (if it be a small one) and comes to rest in the original lagoon 

 entrance. The entrance becomes blocked up, and a wide belt of 

 land is formed upon the lee side of the atoll ; but no barrier 

 reef exists upon the lee side. 



As sand is deposited in the lagoon it tends to obliterate the 

 coral growth, and so a lagoon, that at first tended to become 

 shallow by the upgrowth of coral colonies, ultimately becomes 

 devoid of living coral, and to shoal entirely by the deposition of 

 sediment. In the Cocos-Keeling atoll, the history since 1825 

 shows a steady filling-in of the lagoon. The continuation of the 

 process that formed the perfect atoll, therefore, tends to obliterate 

 the lagoon. The lagoon shores gain on the lagoon water, and 

 banks i-ise up in its shallower parts ; the windward side of the 

 lagoon, if it be of large size, being the first portion to become 

 obliterated. » 



The explanation of the origin of fringing reefs foUov/s the same 

 lines. On any platform that lies above the limiting line of sedi- 

 mentation, reef-corals will develop, when the conditions of the 

 water are suitable. Fringing reefs are merely reefs taking origin 

 upon the submarine slopes of oceanic land, when these slopes afibrd 

 a foothold in the wave-stirred area. 



Barrier-reefs were explained in 1856 by Prof. Le Conte as being 

 fringing reefs of which the growth was " limited on one side by 

 the muddiness of the water, and on the other by the depth." In 

 1884 Dr. Guppy independently furnished the same explanation. 

 This explanation, which is an isolated and discordant thing when 

 "Subsidence" or "Solution" is taken as accounting for atoll 

 formation, becomes of consequence, and falls into line with other 

 ascertained facts, when the importance of " Sedimentation " is 

 appreciated. 



Dr. R. Broom, C.M.Z.S., exhibited an unborn foetus of 

 Chrysochloris hottentota, and two young specimens of C. asiatica, 

 one probably only a couple of days old, and made some remarks 

 on the habits and life-history of the Cape Moles. 



Dr. R. Broom, O.M.Z.S., also exhibited the skulls of two 

 South African fossil reptiles — Lycosuchus vanderi^ieti and Bauria 

 cynops. The former is from the Karroo Beds of Middle Permian 

 age, and is the most perfect Therocephalian skull as yet discovered. 



Since Owen's order Theriodontia was found to contain two well- 



