56 CORAL FORMATIONS, 
of the shore reef, the water slowly deepens, and then there is an 
abrupt descent, at an angle of 40 or 50 degrees. The results of 
earlier voyagers, among whom Beechey stands pre-eminent, correspond 
with this statement. At considerable depths, as would appear from 
the above facts, the sides of the coral structure may be vertical or even 
may overhang the bottom below. 
There are examples also of less abrupt slopes. Northwest of the 
Sandwich Group, Lisiansky, 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 fathoms.* 
Christmas Island affords on its western side another example of gra- 
dually 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 generally continue much beyond the 
distance elsewhere, as was first observed by Beechey. At Wash- 
ington Island, mostly abrupt in its shores, there is a bank, according 
to the surveys of the Expedition, extending from the east point to a 
distance of haif a mile, and another on the west extending to a dis- 
tance of nearly two miles. At Kuria, one of the Kingsmills, soundings 
continue for three miles from the north extremity, along a bank 
stretching off from this point to the north-northwest. Many other 
instances might be cited, but they are seldom as remarkable; yet 
nearly all islands, especially if the points are much prominent, afford 
similar facts. It has been said that the reef to leeward is generally 
less abrupt than that to windward, but no facts were obtained by the 
Expedition sufficiently definite or extensive to settle this question. 
It is probably true, yet the difference if any must be slight. 
ing.—At Heawandoo Pholo (one of the Maldives) Lieutenant Powell found 50 or 60 
fathoms close to the edge of the reef. One hundred fathoms from the mouth of the 
lagoon of Diego Garcia, Captain Moresby found no bottom with 150 fathoms. At 
Egmont Island, 50 fathoms from the reef, soundings were struck in 150 fathoms. At 
Cardoo Atoll, only 60 yards from the reef, no bottom was obtained with a line of 200 
fathoms. Off Keeling Island, 2200 yards from the breakers, Captain Fitzroy found no 
bottom at 1200 fathoms. Mr. Darwin also states that at a depth between five and six 
hundred fathoms, the line was partly cut, as if it had rubbed against a projecting ledge of 
rock; and deduces from the fact ‘ the probable existence of submarine cliffs.” 
* Voyage round the world, in the years 1803-6, in the ship Neva, by N. Lisiansky, 
Captain in the Russian Navy, 4to, London ; pp. 254-257, 
