248 APPENDIX. 



have a less complicated outline), and from their similarity 

 in composition, as may be observed in their upraised 

 portions. The depth within the banks northward of 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 might easily 

 have been caused by a difference in the action of the 

 currents during their formation : moreover, the greater 

 quantity of living coral, which, according to Capt. Moresby, 

 exists on the northern banks, would tend 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 coast, and 

 on the western side in the southern portion, differ greatly 

 from true barrier-reefs wholly formed by the growth of coral. 

 It is indeed the direct conclusion of Ehrenberg ( Uber die, 

 etc., pp. 45 and 51), that they are connected in their origin 

 quite secondarily with the growth of coral ; and he remarks 

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

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

 present a nearly similar appearance. I cannot, however, 

 avoid suspecting, from information given me by Dr. 

 Malcolmson and Capt. Moresby, that Ehrenberg has 

 rather under-rated the influence of corals, in some places 

 at least, on the formation of the tertiary deposits of the 

 Red Sea. 



The West Coast of the Red Sea between lat. 19 and 22 . 

 — There are, in this space, reefs which, if I had known 

 nothing of those in other parts of the B.ed Sea, I should 

 unhesitatingly have considered as barrier-reefs ; and, after 

 deliberation, I have come to the same conclusion. 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 disc), 



