14 Lhosphate Rocks of South Carolina, 
As seen in the foregoing table of the fossiliferous 
beds exposed in South Carolina, the Cretaceous for- 
mation, which belongs to the Chalk age of Europe, 
is the lowest. It is exposed on the banks of the Pee 
Dee River. In boring the Artesian Well, in Charles- 
ton, it was reached at about eight hundred feet below 
the surface, and in the place where it properly belongs 
in the sequence, directly under the Eocene Marl Bed. 
On the Pee Dee it occurs in alternate layers of soft 
Marl and hard Limestone rock; its color is a dark 
blueish gray, though sometimes the limestone is 
yellowish. Cretaceous Marls are poor, they rarely 
contain more than thirty to forty per cent. of Car- 
bonate of Lime. The Limestones of this age, how- 
ever, are rich, varying from sixty to seventy-five per 
cent. In the annexed Plate, No. I, it is represented 
as the lowest stratum. 
Second, in the ascending order, comes the Eocene, 
or oldest bed of the Tertiary Division. It is exten- 
sively developed in South Carolina, especially on the 
Ashley and Cooper Rivers, and therefore called by 
Mr. Ruffin ‘The Great Carolinian Marl Bed,’ and now 
known to be one of the thickest and richest deposits 
of Mart in the world; containing from fifty-five to 
ninety-five per cent. of Carbonate of Lime. It has been 
bored to the depth of seven hundred feet in the 
Artesian Well of Charleston, and though all the strata 
to that depth are homogenous, yet they vary in tex- 
ture, according to the character of the animal remains 
of which they are composed. 
The Marl proper is covered with thin layers of 
