6 SMITHSONIAN" MISCELLANEOUS COLLECTIONS VOL. 149 



The term marine terrace as used here includes terraces formed in 

 estuaries as well as those bordering the open sea. A delta built into 

 tidal waters may be considered a marine feature, though it was built 

 by a river, and may rise a few feet above the contemporary sea level. 

 It is the connecting link between a river terrace and a marine terrace. 



Shore features and delta deposits may yield the only clues from 

 which the former presence of the sea on the land may be inferred. 

 Clean water drops no clastic sediment. Continuous sedimentation 

 across a large, open bay or far from land in the ocean is not to be 

 expected. Every river and little stream dumps its load of sand or 

 gravel at the shore, from which it is distributed across the bottom 

 by waves and currents. So one need not be surprised to find great 

 areas that must have been submerged beneath the sea completely 

 free from recognizable contemporary sediments or covered by only 

 a thin veneer of sand or silt. 



Some geologists deny the marine origin of certain terraces because 

 they find Pliocene or older rocks at the surface within areas claimed 

 to have been flooded during the Pleistocene. They overlook the fact 

 that parts of the Gulf of Mexico off the coast of Florida are floored 

 with bare Eocene limestone (Cooke, 1939, p. 75). Gould and 

 Stewart report outcrops of several other Tertiary limestones in the 

 bed of the Gulf off St. Petersburg and Fort Myers. Dredgings 

 studied by them indicate that ". . . unconsolidated sediments in many 

 places form only a thin veneer on the bedrock surface, whereas in 

 other areas the bedrock is essentially uncovered" (Gould and Stewart, 

 1955, p. 13). If the Gulf were to withdraw to a lower level, the 

 newly emerged Recent terrace would be free from terrace deposits 

 at such places. 



The names of shore lines and terraces should not be applied to the 

 sediments under the terraces unless there is clear evidence that the 

 sediments are contemporaneous with the shore lines. The geologic 

 formation whose upper surface forms a terrace may be much older 

 than the shore line ; if so, the use of the name for those older deposits 

 would not be appropriate. Moreover, the shore line and the terrace 

 are much more extensive than the local geologic unit to which a 

 formation name is applied. 



SHORE LINES ALONG THE ATLANTIC SEABOARD 



Marine terraces were recognized along the Middle Atlantic States 

 as long ago as 1887, when McGee described the Columbia Forma- 

 tion. More detailed work was later done by Shattuck (1901, 1906). 



