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 O. 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 av 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 Reef. But having examined only 
tho 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.! 
* [n the first place, speaking generally, the outline of the Great Barrier 
Reef is parallel to the outline of the northeast coast. Тһе 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 tolerably 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. 
