THE LOWER PIXE BELT, OR SAVANNA REGION. 47 



tensive formation. Reaching from Mazyck's ferry on the San tee in 

 Charleston county to Vance's ferry on that river in Orangeburg county, 

 and underlying nearly the whole of Clarendon county, they have been 

 traced along Potato creek as far north as Sumter county. Westward they 

 extend through Colleton, Orangeburg, Hampton and Barnwell counties, 

 to the Savannah river ; reaching as high up on that stream as Shell blutl", 

 a noted locality in Burke county, Ga. Their northern margin rests on 

 the buhr-stone, and to the west and south they pass under the Ashley and 

 Cooper marls. The Santee marls form the lowest member of the cal- 

 careous strata of the Charleston basin, and was designated by Prof. 

 Tuomey the Coralline bed of the Charleston basin, being composed of 

 the remains of corals and gigantic oyster shells. It consists of strata of 

 soft marl, marl-stone and green sand, and is very rich in carbonate of 

 lime, averaging 90 per cent, of that valuable ingredient of the soil. 



Resting on the Santee marls, and passing out with them beneath the 

 pleiocene and post-pleiocene of the coast under the sea to a great depth, are 

 the Ashley and Cooper marls. Unlike the Santee marls, they contain 

 neither corals or oyster shells, but are composed of minute many cham- 

 bered shells (Polythalamia and Foraminfera). These marls are of a 

 dark gray color and granular texture, sometimes so compact as to render 

 the material suitable for building purposes. Prof. Tuomey mentions a 

 ruined house, erected long ago, by Sir John Colleton, of this material, 

 which reminded him of Portland stone. The marks of the tools upon 

 the walls exposed to the weather were as well defined as if they had been 

 impressed yesterday, and the angles of a tasteful mantelpiece, handsomely 

 moulded and decorated, were as sharp, despite its long neglect, as when 

 first executed. These marls are not so rich as the Santee marls and av- 

 erage only about GO per cent, of carbonate of lime. They have long 

 been known, however, to contain a notable quantity of phosphate of 

 lime, and a great interest attaches to them, as it is the fragments broken 

 from their irregular surface, and rounded by the waves, which have been 

 converted into the nodules rich in phosphate of lime and known as 



PHOSPHATE ROCK. 



The deposits of phosphate rock occur over a wide range of country, 

 reaching from North Carolina to Florida, and extending in some instances 

 as much as 60 miles inland. Vertically, so far as their occurrence in 

 quantities of value economically is concerned, their distribution is con- 

 fined within narrow limits. They are found at the bottom of rivers, 20 to 

 30 feet in depth, and on land they occur at an elevation but slightly 

 above mean high tide, so that the tides of the existing sea, supplemented 



