32 AGRICULTURAL ANALYSIS 



burg type is composed entirely of organic material, that is, lime, 

 clay, silex and iron taken up by marine animals from the water in 

 which they lived and deposited as limestone. 



Toward the end of the Vicksburg epoch a movement in ele- 

 vation began which brought above the sea level a part of the land 

 in the vicinity of Ocala, forming an island or group of islands be- 

 tween Cuba and the mainland, and the evidence is very strong 

 that these low islands, containing numerous lagoons of fresh water 

 and wooded with palms, reeds and other subtropical vegetation, 

 remained as dry land from that time to the present. At the 

 same time the low borders of the continent began to rise above 

 the sea, forming a coastal plain of marshes and lagoons inhabited 

 by tortoises, birds and other shore animals. It is well known that 

 birds, seals and similar animals select for their rookeries, when 

 possible, such islets as those described. Such locations give them 

 security from predaceous animals, and an undisturbed breeding 

 place for their young. 



As phosphoric acid has a greater affinity for lime than carbonic 

 acid, the carbonate of lime in such localities became converted 

 into the less soluble phosphate of lime, and as the process was 

 continued for thousands of years, in all probability, the first steps 

 in the formation of the invaluable phosphate beds of Florida were 

 taken in this way. 



34. Character and Origin of the Tennessee Phosphates. Some 

 of the most extensive and valuable deposits of phosphates in the 

 United States occur in Tennessee. The existence of these deposits 

 in commercial quantities was first pointed out in 1893 and since 

 that time elaborate examinations of the extent and character of 

 the deposits have been made by the U. S. Geological Survey. 19 



35. Classification. The phosphates of Tennessee are divided 



19 Hayes, The Tennessee Phosphates, i7th Annual Report of the Geolog- 

 ical Survey, 1895-96, Part II : 519. 



Hayes, Tennessee White Phosphate, 2ist Annual Report of the Geolog- 

 ical Survey, 1899-1900, Part III : 478. 



Geological Atlas of the U.S., Columbia Folio, Tennessee. 



Hovey, The Production of Phosphate Rock in 1903, Geological Survey, 

 Mineral Resources of the United States, 1903 : 1047. 



