Message #121074

[dhill757]

On the present beach at Edisto a bed of green mud outcrops close to low tide level. During his early investigations in the area Mr. Rutledge discovered bones in this layer of mud. Believing the bones to be fossil he carefully excavated them, pleased with the prospect of obtaining a complete skeleton. To his dismay the skeleton proved to be that of a very modern cow! Since the cow could not have become buried in the mud at the present site of outcrop, this strange occurrence indicates that what is now the beach was once marsh land and that the sea has moved inland a considerable distance within historic times. The ocean exacts a stiff price for our collection of old bones!

A glance at a Hydrographic Chart gives us additional information of interest. The sea off Edisto is very shallow, the "continental shelf" being about 70 miles wide. All the sea bottom within five miles of shore is less than 40 feet deep. If sea level were to be lowered 150 feet the shore would be extended 55 miles! This point is significant and will be referred to later. From actual observations we know little about the materials that form the sea floor but we do know that the flat strip of country forming the present coast is underlain by marine deposits of the Ice Age. From this strip --- known as the Pamlico Terrace --- marine shells have been collected to levels 12 feet above low tide. This assemblage includes a large number of species that live today only in warmer latitudes.1 We shall show later that this fact is not extraordinary, for the shells lived during an inter-glacial epoch when the sea stood higher and the climate was warmer.

 
We do not know the exact thickness of the Ice Age deposits at Edisto Beach but the fossiliferous portion is probably only a few feet thick and probably lies close to sea level. At Coffin Point 10 miles to the southwest, where the Service's core drill put down an exploratory well, we entered sediments at a depth of 72 feet that appeared to be definitely older than the Ice Age. This gives us at least a maximum figure for this general area and one that compares favorably with other drilling records. The deposits of the Ice Age consist of beds of dark mud with some sand and shell. The vertebrate fossils are impregnated with mineral matter and their outer surfaces are stained nearly black by organic material. Some of the larger ones come ashore encrusted with sand and recent marine shells, indicating that they have lain exposed on the sea bottom for some time before being cast upon the beach.