NORTH OF CAPE MELVILLE. 325 



This seemed only to be a narrow ridge, or bank, 

 and at a point bearing N. by E. from Cape Mel- 

 ville, just outside a small opening, aud close in to 

 the breakers, it required 135 fathoms to touch the 

 bottom. 



From the neighbourhood of Cape Mel villi* the 

 line of the outer Barrier runs first N.N.W. 

 and then N. by W. for 120 miles, or to the lat. 

 of 12° 20', preserving a distance of about thirty 

 miles from the main land. Throughout this space 

 the Barrier is formed by an exceedingly narrow 

 chain of reefs, many of which are not more than 

 200 or 300 yards wide, while they are from two to 

 twelve miles long. The passages between them arc 

 generally small, but two have a width of nearly three 

 miles, one in lat. 13* 27* south, and another in 

 13° OS'. 



Inside this Barrier is a clear channel between it 

 and the inner reefs, from seven to twelve miles 

 wide. The depth of this channel is everywhere 

 about 1,5 or 20 fathoms, the bottom being almost 

 entirely covered with broken plates of a small dis- 

 coidal coral,* and of corallines belonging to the 

 genus halimcda and others. Among the inner reefs 

 the bottom is coarse coral sand, but inside them, in 

 an irregular, narrow, and shoal channel between 



* I suffer this to stand as it is in the text, because it gives the 

 best popular description of these substances. I am informed, 

 however, by Professor Forbes, that these coral-like plates are pro- 

 bably of vegetable origin— disks oF acetabularia. 



