APPENDIX. 241 



distance of a quarter of a mile from the shore, and has 

 within it from six to ten feet water : this then is a fringing 

 reef, and is coloured red, From Juba, a little S. of the 

 equator, to Lamoo (in 2 20' S.) "the coast and islands are 

 formed of madrepore " (Owen's Narrative^ vol. i. p. 363). 

 The chart of this part (entitled Dundas Islds.) presents an 

 extraordinary appearance ; the coast of the mainland is 

 quite straight, and it is fronted at the average distance of 

 two miles by exceedingly narrow, straight islets, fringed 

 with reefs. Within the chain of islets, there are extensive 

 tidal flats and muddy bays, into which many rivers enter; 

 the depths of these spaces varies from one to four fathoms 

 — the latter depth not being common, and about twelve 

 feet the average. Outside the chain of islets, the sea, at 

 the distance of a mile, varies in depth from eight to fifteen 

 fathoms. Lieut. Boteler (JVar., vol. i. p. 369) describes the 

 muddy bay of Patta, which seems to resemble other parts 

 of this coast, as fronted by small, narrow, level islets formed 

 of decomposing coral, the margin of which is seldom of 

 greater height than twelve feet, overhanging the rocky 

 surface from which the islets rise. Knowing that the islets 

 are formed of coral, it is, I think, scarcely possible to view 

 the coast, and not at once conclude that we here see a 

 fringing-reef, which has been upraised a few feet : the 

 unusual depth of from two to four fathoms within some of 

 these islets, is probably due to muddy rivers having pre- 

 vented the growth of coral near the shore. There is, how- 

 ever, one difficulty on this view, namely, that before the 

 elevation took place, which converted the reef into a chain 

 of islets, the water must apparently have been still deeper ; 

 on the other hand it may be supposed that the formation of 

 ' a nearly perfect barrier in front, of so large an extent of 

 coast, would cause the currents (especially in front of the 



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