hill] A LESSON ON FOSSILS 399 



The Gulf Stream helps in this land making by bringing sediment 

 and debris which are caught and held by the reefs and which is 

 deposited in the channel between the reef and the Keys. This 

 will become a narrow channel with mud flats like that between the 

 southern end of Florida and the Keys. The present channel 

 will then become new Everglades and be added to the coast of 

 Florida. Another proof that Florida has gained much of her land 

 through the help of the corals is the fact that coral reef rock has 

 been found as far north as St. Augustine. At least twice have 

 Everglades been made and added to the land of the peninsula. 



The steps in adding land, thus to Florida, are these: First, 

 a reef is formed, by corals which build up the surface. Next, 

 waves by leaving material which they carry, build it up twelve 

 or fifteen feet above the water, and become keys. Third, mud 

 and other material, form the peninsula on the north side and the 

 reef, or keys on the South fill up the channed between the shore 

 and new Everglades are formed. In this the mangrove trees help. 

 A line drawn from St. Augustine to Tampa will represent the 

 oldest reef formed. Another new coral reef has meantime begun 

 to be formed farther to the south. Corals will not grow in muddy 

 water, nor in water more than a hundred feet deep, nor in water 

 that ever becomes cooler than 68 ° F. 



It must be said that not all coral reefs add to the land in just 

 this way, but they have done so in the case of Florida. 



Leaf Fossils 



The leaf fossils are not found in the limestone rocks, but in 

 shales which are just mud and clay which have been hardened 

 into rock. Mud flats were formed where rivers emptied into the 

 sea and along rivers grew trees and other plants just as now. 

 Their leaves fell into the streams and drifted down to the mud 

 flats and probably some grew near the flats. Mud is fine material 

 brought down by rivers as any of you can prove by dipping up a 

 tumbler full of water when the stream is in flood, as in spring, or 

 after a great rain and watching the mud settle to the bottom. So 

 little by little the leaves became covered by more mud and there 

 rested until the mud became shale, and the leaf fossils remain in 

 the shale to tell us what sort of plants grew in these ancient times. 



The long story of life upon the earth is a fascinating one. 

 Sometime if you study geology you will know all about it. 



