2ti2 The American Geoloyist. October, 18% 
regularly or irregularly i)ile(l together in great stratified 
masses like walls of masonry, here intact and there more or 
less broken down. Sometimes earthy matter is interlaminated. 
The material is easily quarried, picked out in blocks without 
blasting. All the stripping recpiired is the removal of the 
soil. The rock has mu(!h the appearance of chert, such as is 
often liberated from cherty limestones by the leaching awaj' 
of the calcareous part. This resemblance to chert has led to 
its being passed over without receiving attention. In some 
places, indeed, it is associated Avith chert, the two usually be- 
ing confounded. 
An analysis, made in Atlanta by Mr. J. M. McCandless, 
gave : 
Calcium Phosphate (bone phosphate) 77.54 
Iron and Alumina 1.50 
Calcium Carbonate 6.83 
Other analyses made in Nashville, show the calcium phos- 
phate to range anywhere from 60 to 81 per cent., with vary- 
ing percentages of iron oxide and alumina, but usually' 
within the limits required. 
Whence comes this phosphate ? This involves two ques- 
tions. First, whence come the layers of phosphate rock as 
we find them, and secondly, whence the calcium phosphate of 
which they are composed ? 
First, as to the origin of the layers : the}' are evidently 
a residuum left after a natural leaching of certain highly 
phosphatic limestones. The leaching -has come from the long- 
continued action of atmospheric waters upon the limestones, 
the carbonated waters sinking through the soil and, under the 
cover of the soil, dissolving away the calcium carbonate, 
leaving the less soluable layers of phosphate. 
The limestones yielding the phosphate are undoubtedly of 
Trenton age. Among the divisions of the Nashville rocks of 
this age we have the following : 
1st. The Orthls Bed. This represents a horizon easil}' 
recognized throughout the Silurian Basin of Middle Tennes- 
see. The bed is about 60 feet thick. It gets its name from 
the fact that some of its layers are almost wholly made up of 
the shells of Orthis testudinaria. 
2d. Next above the Orthis bed is the Capitol limestone, 
a granular, current-formed, and hence laminar limestone 
