2gO T. O. MABRY 



this deposit above the larger water courses, such as the Talla- 

 hatchie and Yocona rivers, between which it lies and down 

 whose swifter waters most of the icebergs probably traveled, 

 renders it hardly probable that the deposit was formed in this 

 way. 



According to Professor Chamberlin the Natchez formation 

 occupies similar relations to the Lafayette and to the Loess of 

 the northern Mississippi, though it contains crystalline pebbles 

 in addition to materials derived from the Lafayette ; and he 

 suggests that both may have been formed at the same time, the 

 two representing a distinct episode, or epoch, between the 

 Lafayette and yellow loam. 



On this hypothesis there was a period of upheaval succeed- 

 ing the Lafayette deposition, during which all formations then 

 •existing were greatly eroded. This was followed by subsidence 

 in the region of the lower Mississippi, accompanied by the 

 deposition of the Natchez formation and of the stratum between 

 the Lafayette proper and the Yellow Loam in this vicinity. Then 

 followed an interval of upheaval and erosion, marked by the 

 irregular contours of the upper surface of the bowlder stratum 

 of the Oxford section and by the presence of an old soil at the 

 summit of the Natchez formation. It is not to be understood, 

 however, that the supposed Natchez subsidence was great 

 enough to submerge the areas in question below sea level, for 

 the deposits have not the characteristics and distribution which 

 would probably have resulted from the action of ocean waves. 



The deposits were probably formed when the land surface 

 was at a comparative base level, and are of fluvial and lacus- 

 trine origin, and not marine, nor even estuarine. The amount 

 of geological time represented by this hypothetical oscillation 

 (during which the Natchez formation and its supposed con- 

 gener in this vicinity were deposited and subsequently eroded 

 prior to the deposition of the Loess and the Brown Loam) is 

 probably very short, though it serves to emphasize the time 

 interval between the Lafayette and the Brown Loam. 



5. Other evidence bearing on the age of the Lafayette, and 



