INTRODUCTIOX. XXXI 



been published of ^lacclesfiekl Bank.' the one showing a steep fall to a 

 depth of about 100 fatlionis. preceded by a very gradual slope to the fifty 

 fathom line and a more gradual slope from the 100 to the 700 fathom line. 

 The otlier. nearly at right angles, shows a longer upper slope to the fifty 

 fathom line and a less steep slope to 400 fathoms than the corresponding 

 depths of the first section. 



The leo-end of the chart (PI. 234) whicli has been prepared to illustrate 

 the distribution of the coral reefs in the Pacific requires some additional 

 explanation. 



Many of the volcanic islands represented as without belts of elevated 

 limestones have unimportant patches of fringing reefs; these have not 

 been noted, having no important bearing on the question of the theory 

 of the coral reefs. They are such islands as the Bonin Islands and other 

 volcanic islands north of the Ladrones extending toward Japan, and .some of 

 the Sandwich and Marquesas Islands. 



Volcanic islands, like those of the Society, Cook, Fiji, or Caroline Islands, 

 which are colored blue with a yellow ring, indicate the presence of barrier 

 and of fringing reefs. Islands partly volcanic and partly elevated limestone, 

 as in the Lau group of Fiji, or in Tonga, are also surrounded by fringing 

 and barrier reefs, or reef fiat platforms. Elevated coralliferons limestone 

 i.slands are similarly surrounded in part by fringing reefs or by reef flat 

 platforms and barrier reefs. This is the case in elevated islands with sinks. 

 or in elevated islands which have been eroded to the level of the sea, the 

 land rim of which surrounds a sound ; the underlj-ing base of barrier and 

 fringing reefs of the elevated islands being tertiary limestones. 



Islands and groups colored vellow indicate low atolls elevated perhaps 

 a few feet, but of which the land rim consists of modern reef rock or con- 

 glomerate or breccia, the imderlying base of which is not known. 



The Great Barrier Reef of Australia and its extension along the coast 

 of New Guinea to the Louisiade Archipelago, as well as the barrier reef of 

 New Caledonia, i-; colored to indicate that these barrier reefs are probably 

 underlaid by the submarine extension of the rocks of the adjacent shores. 



' China Sea. Report on the Results of Dredgings obtained on the Macclesfield Bank; Admiralty, 

 1894, 3 Charts. 



