AGASSIZ: BAHAMAS. 185 



with the rate of growth of its coral reefs. Off the west and northwest 

 coasts of Austi-alia, to the north of Houtman's Abrolhos there are exten- 

 sive coral reefs surrounding adjoining islands and skirting the shores of 

 the Australian continent. From their appearance on the Hydrographic 

 Charts they bear a certain resemblance to the reefs of Yucatan, Hon- 

 duras, .and the Mosquito Coast, extending as they do out on the com- 

 paratively shallow continental platform of that part of Australia. 



One cannot fail to be struck with the general resemblance of the Keel- 

 ing atoll described by Darwin, and of which a chart is given by Guppy 

 in his article on the Cocos-Keeling Islands in the Scottish Geographical 

 Magazine for June, 1889, to some of the smaller of the Bahama Banks. 

 The tilling up of the interior lagoon from the sand driven in through the 

 narrow and shallow passages between the islands edging the bank, and 

 perhaps also from the disintegration of the islands themselves, will in 

 time produce, as suggested by Guppy, a bank, the interior of which will 

 be entirely choked by sand, while corals will continue to thrive in the 

 northern part of the lagoon in numerous patches, much as they do in 

 the Bahamas, where their growth is not affected by the movement of 

 the bottom, or by the sand held in suspension during heavy weather. 



The sunken banks of the Bahamas, the Navidad, Silver, and Mouchoir 

 Banks, remind us of the Great Chagos Bank, although there is no evi- 

 dence to show that these banks owe their peculiar shape to the growth 

 of corals due to subsidence, but merely that by subsidence what was once 

 a flourishing coral i-eef edging a marine bank is now by subsidenoe left at 

 a depth at which corals can no longer thrive, while they still flourish and 

 grow on the edges and interior floors where the subsidence has not been 

 great enough to sink that part of the bank to as great a depth, or in other 

 localities where little or no subsidence has taken place. 



The Bahamas can hardly be said to have lagoons in the sense in which 

 we understand an atoll lagoon. With the exception of the lagoon of 

 Hogsty Reef, the lagoons of the Bahamas are either huge sinks or slop- 

 ing faces extending from the inner side of islands on the edge of the 

 banks towards their open side, or they are small salt sinks like the lakes 

 of Ne.w Providence, the lagoon of Watling, and the many salt ponds ex- 

 isting on Long Island, on Inagua, on Grand Turk Island, and others. 



On the Great Bahama Bank the only sinks which are enclosed by 

 higher banks are the extensive depression between New Providence and 

 Eleuthftra, with a greatest depth of six fathoms near Eleuthera, and the 

 two to the west of the line of cays between Highborn Cay and Harvey 

 Cay, with a maximum depth of four and a quarter fathoms. On the 



