NATURAL OCCURRENCE OF PHOSPHATES 27 



this, the shallow sea contained innumerable sharks, manatees, 

 whales, and other inhabitants of tropical waters, and the remains 

 of these animals added to the phosphatic store. 



While these changes were taking place in the quarternary 

 period, the Florida peninsula was gradually rising, and as soon 

 as it reached a considerable height the process of denudation by 

 the action of water commenced. Then there was a subsi- 

 dence and the peninsula again passed under the sea and was cov- 

 ered with successive layers of sand. The limestone during this 

 process had been leached by rain water containing an excess of 

 carbon dioxid. In this way the limestone was gradually dis- 

 solved while the insoluble phosphate of lime was left in suspen- 

 sion. During this time the bones of the animals before men- 

 tioned by their decomposition added to the phosphate of lime 

 present in the underlying strata, while some were transformed 

 into fossils of phosphate of lime just as they are found to-day in 

 vast quantities. 



Wyatt explains the phosphate deposits somewhat differently. 15 

 According to him, during the miocene submergence there was 

 deposited upon the upper eocene limestone, more especially in 

 the cracks and fissures resulting from their drying, a soft, 

 finely disintegrated calcareous sediment or mud. The estuaries 

 formed during this period were swarming with animal and vege- 

 table life, and from this organic life the phosphates were formed 

 by decomposition and metamorphism due to the gases and acids 

 with which the waters were charged. 



After the disappearance of the miocene sea there were great 

 disturbances of the strata. Then followed the pliocene and ter- 

 tiary periods and quarternary seas, with their deposits and drifts 

 of shells, sands, clays, marls, bowlders, and other transported 

 materials supervening in an era when there were great fluctua- 

 tions of cold and heat. 



By reason of these disturbances the masses of the phosphate 

 deposits which had not been infiltrated in the limestone became 

 broken up and mingled with the other debris and were thus de- 

 posited in various mounds or depressions. The general result 

 16 Engineering and Mining Journal, 1890, 50 : 218. 



