KED SEA. 253 



lat. 17° is usually greater, and their outer sides shelve more 

 abruptly (circumstances which seem to go together) than in 

 the Dhalac and Farsan archipelagoes ; but this may have been 

 caused by a stronger action of the currents during their forma- 

 tion : moreover, the greater abundance of living coral on the 

 northern banks, tends to give them steeper margins. 



From this account, brief and imperfect as it is, we can 

 see that the great chain of banks on the eastern side of the 

 Red Sea, and on the western side of the southern portion, 

 differ greatly from true barrier-reefs, which are wholly formed 

 by the growth of coral. Ehrenberg also concludes (Ueber die, 

 &c. pp. 45 and 51) that these banks owe their origin in a 

 quite secondary manner to the growth of coral. He remarks 

 that the islands off the coast of Norway, if worn down level 

 with the sea, and merely coated with living coral, would pre- 

 sent a nearly similar appearance. It seems, however, from 

 information given me by Dr.Malcolmson and Captain Moresby, 

 that Ehrenberg has rather under-rated the influence of 

 corals on the formation of the tertiary deposits of the Red 

 Sea. 



The West Coast of the Red Sea between Lat, 19° and 22°. 

 — Reefs exist here, which, if I had known nothing of the 

 others in the Red Sea, I should unhesitatingly have considered 

 as barrier-reefs. One of these reefs, in 20° 15', is twenty 

 miles long, less than a mile in width (but expanding at the 

 northern end into a disk), slightly sinuous, and parallel to the 

 main land at the distance of five miles from it, with very deep 

 water inside, so that in one place soundings were not obtained 

 with 205 fathoms. Some leagues farther south, there is 

 another very narrow reef, ten miles long, with other small 

 portions of ree/, north and south, almost connected with it ; 

 and within this line of reefs (as well as outside) the water is 

 profoundly deep. There are also some small linear and sickle- 

 formed reefs, lying a little way out at sea. All these reefs are 

 covered, as I am informed by Captain Moresby, by living corals. 



