292 T. O. MABRY 



sippi valley, presented by them in the article just referred to, 

 appears conclusive. 



I have shown that the Yellow Loam occupies the same 

 position with reference to the Lafayette in the interior, that 

 the Loess does along the Mississippi valley. By the foregoing 

 considerations, and by a review of the relation of the Yellow 

 Loam to this loess in this vicinity, I hope to strengthen the 

 evidence already presented by McGee that the Yellow Loam 

 and the Loess are not only homotoxial but that they are also 

 genetically related. 



B. The relation of the Brown or Yellow Loam to the Loess [or 

 Bluff formation of Hilgard). — These two deposits were discrimi- 

 nated by Hilgard, who considered them as separate formations, 

 the Brown Loam being the younger (Ag. & Geol. of Miss. i860). 



Later, McGee and others have noted the somewhat complex 

 relations of the two along the bluffs of the southern Mississippi, 

 especially around Vicksburg and Natchez {12th Ann. Rept. 

 U. S. Geol. Surv., p. 392 etseq.). 



The present paper has nothing to do, except in a very gen- 

 eral way, with this area, concerning which McGee says: "The 

 loess of the lower Mississippi region may be characterized as a 

 peculiar condition of the Brown Loam, or as an imperfectly 

 demarked phase of the great formation into which both deposits 

 fall." Having reached the same conclusion from a study of the 

 area embraced within the scope of this paper I shall now 

 proceed to state the grounds on which this opinion is based : 



1. The Drift of the North is the surface formation, to which 

 the loess of the river valleys bears an ascertained and definite 

 relation, as already noted. During the Glacial period there 

 were extensive continental oscillations during which, according 

 to some authorities, the whole southern part of our continent 

 was submerged: so, on a priori grounds, we should find as the 

 " southern equivalent of the northern Drift " a mass of water- 

 deposited sediment more commensurate in quantity with the Drift 

 than is the Loess alone. Evidence of such submergence will be 

 brought out in the further discussion of this subject. 



