68 The Phosphates of America. 



level, and it was covered by successive deposits of sand, varied l>y 

 clays, the beach being the red clays of northern Florida and south- 

 ern Georgia. 



Before this took place, however, an economic change bearing on 

 this subject had occurred. In many places the limestone, then the 

 dry land, had been leached by the rain-water even as chalk to-day 

 can be leached, and is leached, by water containing more or less 

 carbonic acid. The highly phosphatic limestone was denuded and 

 dissolved, the bicarbonate of lime carried away in solution and the 

 more insoluble phosphate in suspension. In the stiller waters of 

 the estuaries and in the wider river beds (the river had the same 

 course as now, broadly speaking) the phosphate of lime in suspen- 

 sion was deposited as an alluvial secondary deposit. This was 

 mixed, of course, in many places with lime, sand and clay brought 

 clown by the same waters. 



While all this was in action, above the limestone were the bones 

 of the various beasts and fishes killed by the awful cold and by 

 overcrowding. Some of these bones helped by their decomposition 

 to add to the phosphate of lime present in the underlying strata, 

 and some were pseudomorphed into fossils of phosphate of lime, 

 just as we find them. to-day in vast quantities ; some were washed 

 down and were deposited with the phosphatic mud, and some are 

 still in situ in the clay overlying the limestone or mixed with the 

 shell reefs and beaches. 



Our own conclusions took precedence of both these opinions, and 

 were published in the Engineering and Mining Journal of August 

 23, 1890. We then argued and still believe that during the miocene 

 submergence there was deposited upon the upper eocene limestones, 

 more especially in the cracks or fissures resulting from their drying 

 up, a soft, finely disintegrated calcareous sediment or mud. 



The gradual evaporation of these miocene waters brought about 

 the formation, principally in the neighborhood of the rock cavities 

 and fissures, of large and small estuaries. These estuaries were re- 

 plete, swarming with life and vegetable matter fish, molluscs, rep- 

 tiles and marine plants. They were, besides, heavily charged with 

 gases and acids, and their continuous concentration ultimately in- 

 duced a multiplicity of readily conceivable processes of decompo- 

 sition and final metamorphism. 



In our opinion they constitute the origin of our Florida phos- 

 phate of lime, and disregarding all other hypotheses, we consider 

 that we are practically contemplating 



