DEPOSITION IN THE SEA 951 
have been formed by the life and death of many salt- 
water-loving trees (p. 460). Certainly, at the present 
time, the mangrove is making a deposit of carbonaceous 
matter which resembles some of the layers of coal. 
Coral Reefs. Everywhere in the ocean and on the 
coasts, animals dwell in large numbers, and many of 
Fie. 141. 
Mangrove trees and swamp on Florida coast. 
them are able to extract carbonate of lime from the 
water. This they build into their shells or skeletons, 
which endure when the softer tissues perish. By this 
life and death of shell-bearing animals, deposits of 
carbonate of lime are accumulating on the ocean bot- 
tom. There are beds of oysters, and also banks of 
shells; but by far the most remarkable deposits of 
