78 FLORIDA GEOLOGICAL SURVEY SIXTH ANNUAL REPORT. 



V 



of these processes, however, are well understood. That normal 

 phosphate is to some extent soluble in soil waters is well established 

 and fully recognized. In the hard rock phosphate section of Flor- 

 ida there is practically no surface drainage, the rain water passing 

 directly into the earth. At a lower level the circulation of the 

 water is interfered with and the water may become stationary or 

 nearly so. The check in circulation is due in some instances to 

 masses and beds of clay which are residual from the disintegrating 

 formations. In any case the movement of the water is checked 

 upon reaching the water line. The relation of the phosphate de- 

 posits to the ground water level, and also the evident and prob- 

 able changes of the water level during geologic time have been 

 discussed in the writer's paper on these deposits previously referreti 

 to. It is thus apparent that there are important changes in the 

 chemical conditions in the earth. Among these may be mentioned 

 the check to the free movement of the water, and the evident 

 mingling of different waters. In this connection the observations 

 of Reese, previously referred to, in which it is shown thit calc'um 

 phosphate in solution in carbonated waters is precipitated when 

 the water stands over limestone, are particularly suggestive. As 

 shown in my earlier papers the hard rock phosphates of Florida 

 are invariably formed directly upon limestone, and need not be 

 sought for elsewhere. Moreover they are thrown out of solution 

 from carbonated waters which pass over and through these lime- 

 stones, the manner of their formation apparently being entirely in 

 accord with Reese's experiments. 



The land pebble phosphate deposits of Florida are probably 

 derived, like the hard rock deposits, from the Alum Bluff forma- 

 tion. The processes by which they have accumulated in their pres- 

 ent form are, however, strikingly different. While the hard rock 

 phosphates, as has been stated, represent chemical precipitates or 

 replacement deposits, the phosphate having been transported to its 

 present location in solution, the land pebble deposits appear to rep- 

 resent materials which are residual from erosion of the parent 

 formation. The hard rock phosphates occur in sections where the 

 parent formation has entirely disintegrated over limestones; the 

 land pebble deposits, on the contrary, are found as a blanket deposit 

 resting upon, and representing a concentration from the parent 

 formation. It thus follows that the matrix of the land pebble de- 



