138 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



" The most remarkable deviations from this condition are in the spaces 

 between Cape Melville and Lizard Island, and at the back of Wreck Bay and 

 Raine's Islet. Now in each of these cases there are islands of granite or other 

 rocks advanced from the mainland, and thus causing an original irregularity 

 in the depth of water, as it would be independent of the coral reef. This is 

 very remarkable in the space between 12° 20' and 11° 30', where we have Cape 

 Grenville, Cockburn Islands, and Sir C. Hardy's Islands, projecting towards 

 Raine's Islet opening, and Fair Cape and Cape Weymouth, with Forbes Island 

 and Quoin Island projecting towards Wreck Bay. Near Sir Charles Hardy's 

 Islands there is also a remarkable narrow channel of deep water, between 

 them and the large Cockburn reef, in which there is a depth of thirty fathoms, 

 while on each side of it is either a reef nearly dry at low water, or a depth 

 not exceeding ten fathoms. This channel is about twenty miles long, rarely 

 more than two miles broad, and it runs in the same direction as the islands 

 lie off Cape Grenville, or about east-northeast, and points in a straight line 

 for Raine's Islet opening." 



It seems to me that Jukes has here struck the correct explanation of 

 the structure of the Great Barrier Eeef. But having examined only 

 the two extremes, he did not perhaps realize that the same condition 

 of things existed off any line in which such islands were found. He 

 allowed his admiration for the simplicity of the explanation of the 

 theory of coral reefs by Darwin to blind him to his own still simpler 

 explanation, which I will here quote. 1 



" In the first place, speaking generally, the outline of the Great Barrier 

 Reef is parallel to the outline of the northeast coast. The one follows the 

 other in all its curves and flexures with quite sufficient conformability to 

 show that the two are connected. This is perceptible even in the small chart 

 attached to this work, but still more remarkably so when the large Admiralty 

 Charts are examined. It is evident that the circumstances that modified the 

 outline of the coast likewise determined the general outline of the reefs. 

 This is nothing else than to say, that the outline of the reefs depends upon 

 the depth of the water. Just as in a large and accurate chart of any line of 

 coast we should find the boundary of any certain line of soundings, such as 

 20, 50, or 100 fathoms, conforming generally to the outline of the coast, fol- 

 lowing its larger flexures and more important features ; so we find the outline 

 of the Barrier Reefs conforming to the northeast coast of Australia. Granting 

 that the mean slope of the rocks, forming the original sea-bottom of this coast, 

 was tolerahly regular and conformable to the slope of the land, it is evident 

 that if we took away the coral reefs and raised the land to any given height, 

 as, for instance, 100 fathoms, we should not greatly alter the outline of the 

 coast, but only shift its situation. It would be thrown so much further for- 



1 Voyage of the " Fly," Vol. I. p. 345. 



