190 GEOLOGICAL SURVEY 
finer and finer. 'The large pebbles are succeeded by gravel and coarse sand, and towards the coast 
these are replaced by the fine sands blown about by the winds. 
The blending of these strata on the surface renders it impossible to distinguish the arenaceous 
beds of the different Tertiary formations, when they do not enclose organic remains. 'The sandy 
beds of the buhr-stone are intermingled with those of the Pliocene, which pass into the superin- 
cumbent beds of the P. Pliocene, and the latter are, in turn, blended with the moving sands 
on the coast. 
Fig. 31 represents a section exhibiting the relative position of the Tertiary beds of the State. 
Fig, 31. 
b 
é ZZ = 
a =F pe 
: SSE Ce a 
c d e 
f—Buhr-stone formation. e.—Santee beds. d.—Coralline marl. ¢.—Ashley and Cooper beds. 6.—Patches of Pliocene. 
a.—P. Pliocene. 
ALLUVIUM.—CHANGES ON THE Coast. 
The deposits included under the term Alluvium are well understood, as comprehending those at 
present in course of formation, such as.the beds formed in lakes, on the banks and at the mouths of 
rivers, and along the coast. In general it is not difficult to distinguish the deposits left, by the 
overflowing of rivers, on their banks, although they differ in various other important respects. 
Without attempting to determine the precise limits of the P. Pliocene and recent deposits on the 
coast, I shall proceed to notice the changes going on there. 
Every one is aware that a vast amount of matter is carried down annually by the rivers into 
the ocean and deposited, in the form of beds of mud or sand. The size of the particles forming 
these beds will depend upon the velocity of the streams transporting them. The coarser materials 
will be deposited first, and by the time the rivers reach the ocean, little besides the finest sedi- 
mentary matter will remain suspended in the water. 'This is one of the causes of the great differ- 
ence that exists in the alluvial soils, seen on the banks of rivers, as we approach their mouths. 
The fine matter held in suspension by the river water, as it enters the ocean, would be dissipated 
by the currents along the coast, if a barrier were not raised by the ocean itself, which breaks the 
force of these currents, and produces still water between the beach and the coast. 
The Gulf Stream produces an eddy current which washes the coast southwardly, and the sand 
bars, so common on the coast, are formed in the diagonal or resultant of these two currents.* 
Those formed at the mouths of rivers must also, it seems to me, be influenced by the force and 
direction of their waters. These bars, however, are generally formed directly by the ocean, and 
not by the water of the rivers. 
* For this and numerous facts relating to the coast, I am indebted to Capt. Bowman, of Fort Sumter. 
