316 
APPENDIX II. 
The case at Tahiti appears to be confirmed by other 
instances ; such as Captain Fitzroy’s sounding (in the 
‘ Beagle ’ Voyage) at Keeling Atoll, 2,200 yards from the 
breakers, when no bottom was found at a depth of 1,200 
fathoms ; and the sounding by Captain Wilkes off Clermont 
Tonnerre (Paumotu Archipelago), where ‘ the lead brought 
up an instant at 350 fathoms, then dropped off and de- 
scended to 600 fathoms, coming up bruised with small 
pieces of red and white coral attached ’ ; as well as that by 
the same ‘ a cable’s length from Ahii,’ where the lead 
struck a ledge of rock at 150 fathoms, and brought up 
finally at 300 fathoms. Still, it would be well that the 
older soundings should be repeated, and the subject be 
more fully investigated. 1 
In regard to Professor Agassiz’s argument that the 
Florida reefs are the result of drifting material (see p. 287), 
and in no way require or indicate subsidence, Professor 
Dana points out that there is little in the great barrier reef 
of Eastern Australia, which has some correspondence in 
position with the sand reefs off eastern North America, to 
suggest a similarity of origin. Full of irregularities of 
direction and of interruptions, it follows in no part an even 
line. In the northern part, the barrier, while varying 
much in its course, is barely 30 miles from the land ; in the 
southern half it extends out 150 miles from the coast, and 
includes a large atoll-formed reef. Further, in the Pacific 
Ocean, the trends, whether of coral island groups, or of the 
single islands, frequently do not correspond with the direc- 
tion of the oceanic currents, or indeed of any current 
depth to which they can bare the bottom, so as to obtain an effective 
broadside stroke, which he thinks rarely exceeds in the most extreme 
cases 20 feet vertical. At 240 feet he believes the displacement of 
the water would be at most only a few inches, and thus the battering 
power would obviously be nil. 
1 See below, p. 319, for an account of Masamarhu Island in the 
Red Sea. 
