STRUCTURE OF CORAL ISLANDS. Wes 
In the Phoenix Group (Plate IX.), depths of 3,000 to 
3,300 fathoms occur, and 3,000 half way between Sydney’s and 
Birnie’s, sixty miles apart; to the southwest of Hnderbury’s 
slopes of 1 : 6 and 1: 3 exist, and to the northeast, of 1: 1:5 
and 1:4. Off Swain’s Island, slopes of 1:7 and 1:13 
were obtained; and off Danger Island (same Plate), 660 
fathoms within half a mile southwest of the reef, and 985 
fathoms one mile east, giving slopes of | : 1 and 1 : 0-75. 
Off the Bahamas, for 400 miles, depths of 2,500 to 3,000 
fathoms occur within twenty miles of the reefs, and at one 
point 2,336 fathoms within two miles, a pitch down of 
1: 0°75. South of central Cuba a depth of 3,428 fathoms exists 
within twenty miles of the Grand Cayman reef, and 3,010 
fathoms within fifteen miles of Swan Island reef. 
There are examples also of less abrupt slopes. Northwest 
of the Hawaian Group, Captain Lisiansky, who commanded 
the Russian ship Neva in a voyage round the world in the 
years 1860-61, at the island bearing his name found shallow 
water for a distance of six or seven miles; the water deepened 
to ten or eleven fathoms the first mile, fifteen the second, and at 
the last throw of the lead there were still but twenty-five fath- 
oms. Christmas Island affords on its western side another 
example of gradually deepening waters. Yet these shallow 
waters terminate finally in a rapid declivity of forty or 
fifty degrees. 
Off the prominent angles of an atoll, soundings gener- 
ally continue much beyond the distance elsewhere, as was 
first observed by Beechey. At Washington Island, mostly 
abrupt in its shores, there is a bank, according to the sur- 
veys of the Expedition, extending from the east point to 
a distance of half a mile, and another on the west extend- 
ing toa distance of nearly two miles. At Kuria, one of 
