Pleistocene to Pre-pleistocene of Mississippi Basin. 369 



Although the lapse of time since the closing stages of the 

 iirst glacial epoch is great, the loess does not appear to have 

 undergone any considerable alteration in Qhemical character 

 since the time of its deposition. Its surface portion for a 

 depth of 4-6 feet, often shows unmistakable signs of oxidation 

 and weathering. Locally, oxidation has penetrated to greater 

 depths. The particles of the surface portion have been disin- 

 tegrated by chemical and physical means, so that they have 

 become notably finer than they were at the time of their depo- 

 sition, and liner than those of the lower portions at the same 

 locality. Were another sheet of loess to be spread over the first 

 to-day, the distinction between the two in later times would be 

 perfectly clear, on account of the chemical and physical changes 

 which the present loess has suffered in its superficial parts. 

 Yet even this distinction would be far less conspicuous than 

 that which now exists between the loess and the surface of the 

 underlying material. This comparison may be in some sense 

 unfair, since it is true that the substratum of the loess and the 

 loess itself are inherently dissimilar ; but it is not that differ- 

 ence which is here insisted upon. It is the degree of altera- 

 tion which the surface of the material below the loess has suf- 

 fered — an alteration such as surface exposure would effect — 

 which is of significance, and this alteration, which must have 

 taken place before the deposition of the loess, is in general 

 very much greater than that which the surface of the loess has 

 undergone since the close of the first glacial epoch. 



In many places there is a thin layer (4-8 feet) of earth 

 above the gravels of the Orange Sand series. This is believed 

 to represent, in many places at least, the last work of the 

 waters which deposited the coarser materials below. It is com- 

 monly somewhat gritty, the gritty element (sand) partaking of 

 the nature of the sand below, but it is distinctly clayey in tex- 

 ture The textural difference between it and the loess is much 

 less than that between the loess and the upper surface of the 

 Orange Sands as commonly developed, but quite as great as 

 that between the loess and the till. But it is in just such situa- 

 tions that the line marking the junction of the loess and the 

 underlying earth is most conspicuous and significant. The 

 latter shows the texture and deep coloration which denote the 

 oxidation and surface alteration that result from long exposure 

 to atmospheric action. In many places the junction of the 

 loess with this layer, is the most obtrusive line in the section. 

 In more than one place, it may be noted in passing, does this 

 super-gravel earth show an eroded surface, upon which the 

 loess rests un conformably, though the degree of unconformity 

 in such cases is often slight. 



