624 TRANSACTIONS OF SECTION E. 



formed from such shoals — and this is probably the case — they show in a marked 

 manner an accompanying increase in depth in their centres by solution, tidal 

 erosion, «fec., some lagoons being 40 to 50 fathoms deep. 



Land on the encircling reefs of atolls may be formed either by the piling-up of 

 coral masses from the reef-flats or by some change of level of the reefs in respect 

 to the sea. Both methods are found in the Chagos, but there is evidence in every 

 atoll of some apparent upheaval. This alteration of level vrould appear to be 

 universal throughout the Indo- Pacific coral-reef regions (lat. 30° N. to lat. 26° S.), 

 the required amount varying from 5 to 35 feet. Since the phenomenon is so 

 widespread, and there is evidence of many local upheavals throughout this zone, 

 it would seem to be due to some withdrawal of water from the Equator rather than 

 to any change in level of the ocean floor. The causes of this are probably to be 

 found partially in the attraction of continental masses on the water, but mainly 

 in the piling-up of ice in the south polar regions. 



The lagoons of the atolls are generally increasing in size at the expense of the 

 land, that in Diego Garcia being fringed for a great part of its circumference by 

 low cliffs. Kemains of land are found at the edges of the Salomon Reefs towards 

 the lagoon, where the bottom drops almost perpendicularly from one to four or five 

 fathoms. This further clearly indicates an enlargement of the basin at the expense 

 of the encircling reef-flats. Boring and land-triturating organisms are almost as 

 conspicuous destructive agents as in the Maldives, and the tides are of great im- 

 portance in removing fine sand and washings from the lagoons. Practically no coral 

 masses are swept off the encircling reefs into the lagoons, growing animals and 

 plants alone tending to fill them up. 



The reefs throughout the Chagos are extending seawards by means of corals 

 and nullipores, the latter acting mainly as consolidating agents, but practically form- 

 ing the whole edge below five fathoms. The foundations forthese — true reef-building 

 corals only live down to 35 fathoms, and nullipores down to 60 fathoms — are formed 

 by masses from the shallower parts of the reef above swept outwards by under- 

 currents. The reefs in fact are everywhere spreading outwards on the piled-up 

 remains of their own organisms. 



The reef animals are as abundant as in the Maldives or Seychelles, but their 

 variety appears to be considerably less. In fact the Chagos is thoroughly oceanic 

 in its reef fauna, showing no trace of any former connection with continental slopes. 

 The land animals and plants are such as might be expected on any isolated 

 oceanic islands, but the vegetation is further restricted owing to the islands being 

 purely of limestone formation. 



4. The Geogra'phy of the South Orkneys and other parts of the 

 Weddell Sea. By R. N. Eudmose Brown. 



5. The Limestone Caves of Western Australia. 

 By Professor W. B. Bottomley. 



The cave country of Western Australia is situated in the south-westem portion 

 of the State, between Cape Naturaliste and the Leeuwin, and extends over an area 

 of some sixty miles. The whole district is honeycombed with subterranean galleries, 

 only a few of which have as yet been explored. All who have visited these caves 

 are enthusiastic over their marvellous features, and those best qualified to express 

 an opinion state that they are infinitely grander than the famous Jenolan Caves 

 of New South Wales, and are unrivalled for their beauty, picturesqueness, and 

 infinite variety in the whole world. 



A drive of twenty miles from Busselton, the terminus of the South Western 

 Railway, 150 miles from Perth, and the first known cave of importance is reached. 



Yailingup Cave. — Entered by a shaft about 30 feet deep, and formed of a 

 series of chambers extending for nearly four miles. Each chamber has its own 



