8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 



referred to the Sunderland. This altitude has since been determined 

 as that of the shore line of the Okefenokee terrace. Besides these, 

 remnants of the Hazlehurst terrace are recognizable in Mobile County, 

 and a large part of western Escambia County is occupied by the Mor- 

 ley terrace. The Silver Bluff and the Talbot are well developed on 

 the Coden quadrangle. Thus all ten of the terraces occur in Alabama 

 at the same altitudes as along the Atlantic seaboard. They form the 

 connecting link with those of the Mississippi Embayment, which 

 adjoins them. 



TERRACES IN THE MISSISSIPPI EMBAYMENT 



Above Little Rock, Ark., the Mississippi Embayment is floored by 

 Quaternary deposits that abut the Ozark Escarpment on the north- 

 west and the Mississippi Bluff on the east. The foot of the scarp 

 from Little Rock to Cape Girardeau, Mo., forms a nearly level 

 line very close to 360 feet above sea level. The base of the bluff on 

 the east is lower because the river has cut into the Quaternary deposits, 

 but many remnants of a plain abut the bluff at 360 feet above sea level. 

 I interpret this 360- foot margin of the Quaternary deposits as the 

 shore line of a bay when sea level in the Gulf of Mexico stood 360 feet 

 higher than now. 



Other horizontal shore lines of smaller bays can be traced at lower 

 levels. They stand at the same heights above sea level as the shore 

 lines in Alabama and along the Atlantic seaboard. At the heads of 

 several of the bays abandoned deltas rise above the general level. 



Morley terrace {shore line 360 feet). — The highest inundation 

 reported here backed water in the pre-Pleistocene valleys in the 

 Mississippi Embayment to a height of approximately 360 feet above 

 present sea level. Tidewater then extended up the gorge of the 

 Mississippi probably as far as Gorham, 111., about 30 miles above 

 Cape Girardeau, which stands at the head of the bay. The valley of 

 the Ohio was flooded for many miles into Illinois and Kentucky. 

 Tidewater may have extended up the Tennessee River to the head of 

 Kentucky Lake (Jeannette, Tenn., quadrangle). 



As shown in figure 1, the shore of the bay extended south westward 

 in a nearly straight line from Cape Girardeau to Little Rock, beyond 

 which it has not been traced. The eastern shore lies high up on the 

 bluff of the Mississippi River and is not so well preserved. It extended 

 past Memphis, Yazoo City, Vicksburg, and Natchez into West Felici- 

 ana Parish, La., where the bay opened into the expanded Gulf of Mex- 

 ico, whose shore extended eastward parallel to the present coast. 



