E. A. Smith — Post-Eocene Formations of Alabama. 287 



Island,* we find the marine or estnarine equivalents of our 

 river terraces, in an ancient deposit with imbedded shells, not 

 of extinct species, it is true, but of species not now inhabiting 

 the same localities. + As we come up the bay coast towards 

 Mobile, we find this marine or estuarine deposit giving place 

 to a blue clay with stumps and roots, underlying several feet 

 of sands and yellow loam, thus assuming the characters of the 

 river terraces. 



The relations of the Quaternary formations of the Gulf 

 States were first clearly defined by Dr. Hilgard,;}; from their 

 exposures along the Mississippi River. In descending order 

 they are as follows : Yellow loam, Loess, and Port Hudson. 

 The first of these, the Yellow loam, is a fine grained siliceous 

 clay with only a moderate percentage of lime, forming the 

 soils over a large area especially in the northwestern part of 

 Mississippi and the adjacent parts of Tennessee, where it may 

 be seen for at least thirty miles from the river bluff. The 

 Loess is a fine calcareous silt which has often been described, 

 and which in this country seems to be confined to the imme- 

 diate drainage area of the Mississippi River, and to be com- 

 posed of materials of Glacial origin. It is strongly calcareous, 

 effervesces with acids, and contains in addition a large amount 

 of carbonate of lime in the form of concretions or " puppets." 

 The loess, unlike the yellow loam, occupies a comparatively 

 narrow belt along the river. The Port Hudson consists of 

 sands with occasional gravel, alternating with greenish or blu- 

 ish clays, which, especially in the lower parts, hold imbedded 

 drift wood, roots, and stumps in most perfect state of preserva- 

 tion. These clays are like the loess, strongly calcareous and 

 contain similar concretions of carbonate of lime. The present 

 channel of the Mississippi lies in general in this stratum, 

 which, tempered by the later deposits of the river, gives rise 

 to the fertile "buckshot " and other soils of the alluvial plain. 



The corresponding deposits along the larger rivers of Ala- 

 bama constitute what are commonly known as the Second 

 Bottoms or Second Terraces. 



These are flat benches, usually not more than a mile in 

 width, and are entirely above overflow except where locally 

 lowered by erosion, and they therefore vary in height from 

 fifty or sixty feet above low water mark along the northern 

 edge of the coastal plain, to not more than ten or fifteen feet in 



* On Mori Louis Island at the mouth of Mobile Bay, we find below the white 

 coast sands, a bed containing oyster shells, and below that a blue clay with 

 stumps and other vegetable remains, thus establishing a connection between the 

 Biloxi of the Coast and the Second Terrace formations of the upper part of the 

 Bay and of the rivers. 



+ D. W. Langdon, Jr., this Journal, vol. xl, p. 237. 



% This Journal, vol. xlvii, Jan., 1869. 



