NATURAL OCCURRENCE OP PHOSPHATES 31 



therefore easily penetrated by the waters of percolation. A 

 good illustration of this is seen on the southwestern and southern 

 edges of Lake Okeechobee. In following down the drainage 

 canal which has been cut into the southwest shore of the lake, 

 the edge of the basin which is composed of this porous material 

 may be seen. The appearance of the limestone would indicate 

 that large portions of it have already given way to the process 

 of solution. The remaining portions are extremely friable, easily 

 crushed, and much of it can be removed by the ordinary 

 dredging machines. Such a limestone as this is peculiarly 

 suited to the accumulation of phosphatic materials due to the 

 percolation of the water containing them. The solution of the 

 limestone and consequent deposit of the phosphate of lime is 

 easily understood w r hen the character of this limestone is con- 

 sidered. 



Shaler as quoted by Eldridge in the work already referred to, 

 refers to this characteristic of the limestone and says that the 

 best conditions for the accumulation of valuable deposits of lime 

 phosphate in residual debris appear to occur where the phos- 

 phatic lime marls are of a rather soft character ; the separate beds 

 having no such solidity as will resist the percolation of water 

 through innumerable incipient joints such as commonly pervade 

 stratified materials, even when they are of a very soft nature. 



Eldridge is also of the opinion that the remains of birds are 

 not sufficient to account for the whole of the phosphatic deposits 

 in Florida. He ascribes them to the joint action of the remains 

 of birds, of land and marine animals, and to the deposition of 

 the phosphatic materials in the waters in the successive subsi- 

 dences of the surface below the water line. 



An important contribution to our knowledge of the origin of 

 Florida phosphates has been made by Dall. 18 After describing the 

 early geological epochs in the southern part of the United States, 

 Dall calls attention to the abundance of foraminifera, whose shells 

 form deposits of limestone, which, in southern Florida, have been 

 found to be nearly 2000 feet in thickness. 



The deposit of rocks which is known geologically as the Vicks- 

 18 The American Fertilizer, 1898, 8 : 108. 



