THE UNDERLYING MARLS. 51 



irregular stratum of loose, gravelly sand only about eight inches 

 in thickness, and containing many bones and fish-teeth, lies 

 what is called the Ashley marl-bed, about two hundred and 

 sixty feet in thickness, as appeared in boring for the artesian 

 well at Charleston, containing about seventy per cent, of car- 

 bonate of lime, the upper surface also containing on an aver- 

 age about ten per cent, of phosphate of lime, received by 

 infiltration from the overlying beds of phosphate rock ; and 

 then comes the Cooper River marl-bed, deposited, of course, 

 previous to the Ashley marl, and greater in age, though of 

 the same geological formation, and filled with vast numbers 

 of hard-shelled mollusca, like the clam and oyster. Its com- 

 position is essentially the same, though it is firmer in texture 

 and lighter in color. Both these strata are rich in the re- 

 mains of fish, especially of the shark family, and contain 

 numerous bones and teeth of cetacean or whale-like animals, 

 many of which were larger than the whales still found in the 

 ocean. 



Beneath the Cooper marl-bed still lies another stratum of 

 marl, known as the Santee bed, deposited at a still earlier 

 period, and composed chiefly of hard shells, corals and coral- 

 lines. This marl is white when dried. The coralline por- 

 tions of this bed contain ninety-four per cent, of carbonate of 

 lime, though there are layers in it of green sand-marl which 

 contain only about twenty-five per cent, of carbonate of lime, 

 with a considerable percentage of potash. This Santee marl 

 contains also gigantic oyster-shells of two very distinctly- 

 marked species, one of which is sometimes twenty-three 

 inches in length, two and half inches wide and three inches 

 thick at the hinge. Each shell of the other species weighs 

 five or six pounds, and is usually as wide as it is long, and as 

 thick as it is broad. It is a most wonderful shell-bed, extend- 

 ing from the Santee to the Savannah rivers. 



The aggregate thickness of these strata, the Ashley, Cooper 

 and Santee marls, is something like seven hundred feet. They 

 all belong to the tertiary period, though differing in age. 

 They have been called the eocene marls, — a term used in 

 geology to denote the dawning of the present epoch. The 

 fossils found in them belong to species of animals not now 

 living, but extinct. Still below these eocene marls of the 



