THE BUILDING OF THE LAND 19 



the greatest depression the sea entered the eastern 

 border of the Everglades. At the same time the 

 reef (which later became the Upper Keys), was 

 still further built up and developed. 



This second subsidence was followed by a 

 second period of elevation, during which the 

 corals of the reef slowly died and the sea again 

 destroyed the surface of the reef, piling up debris, 

 scattering the looser materials, and reshaping it 

 into islands of coral rock. The reef was finally 

 elevated sufficiently for the seeds of dry-land 

 plants to germinate upon it and establish a flora. 

 Lower Florida mainland was doubtless slightly 

 higher at this time than it is at present, sufficiently 

 so that the old land passage elsewhere mentioned 

 from the mainland to the Upper Keys existed. 



A third slight subsidence followed and is prob- 

 ably continuing at present. Now the old landway 

 just referred to is submerged and its remnants are 

 being destroyed by the solvents of the sea. While 

 making excavations in a brackish swamp on my 

 place I found stumps and trunks of live oaks and 

 other trees below the present level of high tide, 

 and these were undoubtedly in the localities where 

 they grew. Sanford mentions seeing a thick 



