39« NATURE-STUDY REVIEW [14:9— Dec, 1918 



that is why in limestone quarries, we often find the remains of 

 shells and corals not destroyed nor much changed from the shapes 

 they bore when they were part of the sea floor. The way in which 

 the soil was made and spread over all the sea rocks is another 

 story; but under all soil lies the solid rock, some of it called lime- 

 stone made by the sea animals whose shells we call fossils, some of 

 it is made in other ways and that is yet another story, but corals 

 and mollusks helped. 



Test limestone with acid and see the bubbles of carbondioxide 



gas set free from the stone. Test a shell and a piece of coral 



with the same acid and see the same gas freed; thus proving that 



the stone and the coral and the shell contain the same substance. 



But just how did the coral and the shells become solid rock, and 



why is not the rock white? As the cooling earth wrinkled, ridges 



with their slopes appeared above the water. At once the rock 



began to be weathered by the action of the air, rains washed off 



the powder thus formed and deposited it as soil. The waves 



broke off pieces of coral; some of the shell-protected animals 



died and their shells and the coral were ground against the rock, 



and a soft dark mud was formed against the edge of the land. 



Shells left by the tide on the surface of the mud became imbedded 



and were gradually covered by other layers of mud and coral 



sand and lay there many thousand years. The mud plain was 



finally raised by more earth wrinkling and become more dry land. 



Sometimes, in this wrinkling, land, that had been above the water. 



was again submerged and more corals and mollusks and crinoids 



and other rock makers lived and died and added their carbonate 



of lime "the coral" to the new rock layer. 



What Corals Have Done for Florida 

 If we look at the map of Florida, we shall see that the Southern 

 portion is occupied by the immense fresh water swamp dotted 

 over with small islands, called "hummocks" covered with vegeta- 

 tion. This swampy region is known as the Everglades. South 

 of the coast line are the Florida Keys which are believed to be the 

 tops of coral islands, because south of these is a living coral reef. 

 When the reef has grown up to the surface of the water the coral 

 animals die and the reef remains a foundation to which are added 

 pieces of broken coral, coral sand, drift wood, sea weed, sediment- 

 brought by the waves and so the keys are made. 



