THE ORIGIN OF CORAL REEFS. 63 
this distinct species must have required thousands of years, and this 
is a strong proof of the antiquity of coral reefs, and of the 
amount of time needed to wear away coral rock. On the question 
of barrter-reefs, especially the barrier-reef of Australia which Dr, 
Guppy has mentioned, I must demur to his supposition that that 
ledge will necessarily extend the whole length of the Australian 
coast. I think it would be much more extraordinary if, for a dis- 
tance of over 2,000 miles, there was the same width of ledge the 
whole way, than that at a certain point the ledge should widen out. 
As Dr. Guppy truly remarks, different effects might be produced by 
breaker action and also by the slope of the land on which the breakers 
impinge, and where you get either a varying nature of the rock or 
a varying nature of the sea. Down on the southern part of the 
coast, the sea is very much heavier,—there is there a tremendous 
sea ; but on the other part of the coast you only get the trade wind, 
which blows parallel to the coast, so that one can, to a certain 
extent, imagine that the bank here on the southern portion of this 
part of coast should be wider; the ledge on the north would be 
narrower in consequence of the comparative smoothness of the sea, 
unless the rock on the coast is softer. I did not quite follow the 
author’s argument of the growth of coral reefs in reference to his 
theory that the reef started on the edge and did not grow out from 
the land. I do not see that that would make the ledge wider above 
than it is farther down. There is another point; but the author is, 
probably, not in a position to-be aware of it, because soundings have 
only recently been taken. He mentions that soundings are wanted. 
They were obtained only a few months ago, and have not been 
published yet, though I have had access to them. We got sound- 
ings out from the coast, showing that the slope is very gradual, and 
that the reef is not actually at the edge, but begins where the depth 
becomes about thirty fathoms. It approaches the land very closely 
to the north, and the reef is one narrow line, comparatively close to 
the shore, and the ledge is about the same width as it is down at 
the south of Australia. 
Mr. Joun Murray (of the Challenger Expedition)—I have 
listened with pleasure to this excellent paper, which suggests 
many questions, and, while with some of Dr. Guppy’s contentions I 
agree, there are others with which I disagree to some extent. 
Perhaps one gets the best conception of what one has written when 
one hears it discussed by other people. The author has pointed out 
‘to-night, what he thinks a most important point, a matter which, 
