Tennessee Pjiosphate Inijusiky. 75 



of tri-basic phosphate of Hme is being mined by the Charleston 

 Mining & Manufacturing Company. Forming, as the material 

 does, one of the rock layers of the country, it is mined as a flat 

 lying coal seam is mined. The method of mining has not changed 

 appreciably, and we may dismiss it, for our purposes, without fur- 

 ther notice. 



Lying geologically below this, but in an entirely different terri- 

 tory, namely, along both sides of the Tennessee River and ad- 

 jacent streams, occurs the so-called white phosphate, which ap- 

 pears to be analogous in its methods of formation, and in its oc- 

 currence, to the hard phosphate rock of Florida, with the impor- 

 tant difference that it occurs in the Niagara member of the Silur- 

 ian instead of a Tertiary limestone. A further important differ- 

 ence is that it is not so widely distributed as is the hard rock of 

 Florida. It has given rise to no important industry. 



In the Ordivician occur the really important horizons of phos- 

 phate rock in Tennessee, leaving out of consideration certain 

 economically unimportant deposits. These all owe their origin 

 to the occurrence of a phosphatic limestone. When this limestone 

 is free, or comparatively free, from other ingredients than car- 

 bonate of lime and phosphate of lime, its disintegration under 

 sub-aerial conditions gives rise to an economically important phos- 

 phate of lime deposit, through the removal of an easily soluble 

 carbonate, and the leaving behind of the more difficultly soluble 

 phosphate. Of very minor importance in the formation of these 

 deposits is the transport in solution from the other portions of the 

 bed of limestone phosphate, and its redeposition through an inter- 

 change of constituents in solution in the lowest portions of the 

 deposit. Of course, any clay or sand in the original limestone re- 

 mains behind when the carbonate of lime is leeched out, with the 

 result of a more or less phosphatic leeched layer containing one 

 or the other of these materials; and it may be said, broadly speak- 

 ing, that to the discovery of methods of utilizing certain of such 

 deposits is due the revolution of the phosphate industry to which 

 I have alluded above. 



The normal aspect of a deposit of this so-called Tennessee 

 brown rock is that of a loosely built wall of dry masonry, the 

 irregular plates of hard phosphate rock lying fairly close to one 

 another and separated only by a sandy layer of the same material. 



