STRUCTURE OF CORAL ISLANDS. 171 
current, especially during the ebbing tide. At Depeyster 
Island, it was found to run at the rate of two and a half miles 
an hour. It was as rapid at Raraka, in the Paumotus, and, as 
Capt. Wilkes remarks, it was difficult to pull a boat against 
tt into the lagoon. 
Il. SOUNDINGS ABOUT CORAL ISLANDS. 
The water around coral islands deepens as rapidly and in 
much the same way as off the reefs about high islands. The 
atoll usually seems to stand as if stilted up in a fathomless sea. 
The soundings of the Expedition afford some interesting re- 
sults. 
Seven miles east of Clermont Tonnerre, the lead ran out to 
1,145 fathoms (6,870 feet), without reaching bottom. Within 
three quarters of a mile of the southern point of this island, the 
lead, at another throw, after running out for a while, brought 
up an instant at 350 fathoms, and then dropped off again and 
descended to 600 fathoms without reaching bottom. On the 
lead, which appeared bruised, a small piece of white coral was 
found, and another of red; but no evidence of living z00- 
phytes. On the east side of the island, three hundred feet 
from the reef, a bottom of coral sand was found in 90 fathoms; 
at one hundred and eighty feet, the same kind of bottom in 85 
fathoms. 
Off the southeast side of Ahii (another of the Paumotus), 
about a cable’s length from the shore, the lead, after descend- 
ing 150 fathoms, struck a ledge of rock, and then fell off and 
finally brought up at a depth of 300 fathoms. 
Two miles east of Serle’s Island, no bottom was found at 
600 fathoms. 
A mile and a half south of the larger Disappointment 
Island, there was no bottom at 550 fathoms. 
