300 T. O. MABRY 



Archaean highlands between Canada and the United States, 

 eroding in some places and in others depositing till ; and if the 

 final retreat of the same ice mass beyond the same highlands 

 be considered as marking the close of the Glacial period, how 

 shall we fix the limits of a formation in the south derived largely 

 from glacial debris? Such deposits, no doubt, are still forming 

 to some extent near the edge of the drift-covered area ; and the 

 deposit of till in the North must have begun in advance of the 

 deposition of the Loess-Loam, and of the Natchez formation. 



We may only say that the Loess-Loam in this region is homo- 

 taxial with the drift, that being composed largely of drift 

 materials it cannot antedate the latter and that the two were in 

 a general sense synchronous. 



C. Conditions tinder which the formation was deposited. — For a 

 discussion of the conditions under which the Loess-Loam was 

 deposited the reader is referred to 12th Ann. Rep. U. S. Geol. 

 Surv., pp. 401-404. 



This formation is to be considered as being essentially a 

 flood-plain deposit of glacial debris (worked over to some 

 extent perhaps by the wind), and formed during a period of 

 subsidence, when the whole surface of the country in this region 

 was practically at sea level. The submergence of the surface 

 seems to have been so slight that fresh-water conditions pre- 

 vailed over marine, and currents laden with glacial debris ran 

 far southward into a tideless bay. Indications, however, of 

 brackish, or of marine conditions, are to be found in the present 

 "salt-licks" which occur quite frequently in the Yellow Loam 

 of some localities, such as Tate and Panola counties. 



In the absence of shore lines to mark this incursion of the 

 sea, evidence of submergence is to be found in the areal and 

 vertical distribution of the formation, which no other causes 

 seem competent to explain. Still more direct evidence is 

 afforded by the presence in some localities of huge foreign 

 bowlders imbedded in, or at the base of, the Yellow Loam, and 

 which, it seems, could only have reached their present positions 

 by iceberg action, or through some supernatural agency. A 



