L. C. Johnson — Phosphate Fields of Florida. 501 



This pit is 38 feet deep, from the top of sandy soil, to the 

 cavity at the base. It is 28 feet across between the tops of the 

 pinnacles, which are 2 feet apart at the base, where the cavity 

 opens. The " plate-rock " is the thin layer next the limestone 

 shoulder imbedded in the interior matrix of " soft-phosphate " 

 — a little argillaceous. This 



"Plate-rock" carries 79^ percent tribasie phosphate of lime. 



The soft phos. matrix " 69 " " " " " 



Attention is called in this section : 



(1) To the " overburthen " of surface sand which, on the 

 tops of the pinnacles of limestone, is approximately 4 feet, 

 while in the center it is sunken and grades to 8 feet in depth. 



(2) To the filling between the pinnacles, which is chiefly 

 " soft-phosphate," a substance of clay-like appearance and con- 

 sistency, of a creamy color. It is very variable in its phos- 

 phate of lime — often high in alumina and iron. In this 

 instance it is a 69 per cent phosphate. 



(3) To the comparatively small portions, 1-3 feet thick 

 next the limestone sloping walls, containing the angular frag- 

 ments of "plate-rock." This portion of the deposit alone is 

 considered of commercial importance. In working the mine, 

 the matrix, however rich in phosphoric acid, is washed away. 



(-1) To the opening at the bottom, between the base of the 

 pinnacles, connected with a subterranean drainage. This is 

 not universal in all the pits, but so general, as in those at 

 Anthony, that it may be considered as a phenomenon of all 

 the deposits in this elevated region. When the elevation is 

 small, as at "Welshton, no opening to take off the leachings has, 

 as yet, been observed. However, mining there has progressed 

 but little. 



(5) The "pinnacles" are evidently upward projections of 

 the bed-rock Eocene limestone of the country. They are 

 seen in these excavations (and in all of them' except one great 

 pit of the Pen. Phos. Co. northward of Sparr) without defi- 

 nite order or arrangement and of all sizes and shapes. The 

 walls are often sloping as in the figure, often vertical and 

 eroded into hollows and into deep round wells or pot-holes, 

 washed out by the waves of a restless sea. 



It would be tedious to enumerate all the mines in this 

 region, and comment on the peculiarities of each, and it would 

 serve no general purpose. Suffice it to say, the variations are 

 principally in the phenomena of erosion, both before and sub- 

 sequent to the deposition of the phosphates. Of these the 

 general facts are about the same. 



Reference has been made to the occurrence of fossils within 

 the workable deposits. There are none, with only one excep- 



