Pleistocene to Pre-jpleistocene of Mississippi Basin. 371 



humus-stained material of the pre-loessial surface, as we inter- 

 pret the phenomena, and are to be sharply discriminated from 

 the loess, with which, except in the matter of position, they 

 have nothing to do We fully concur with Professor Hilgard 

 in his conclusion that this material " unquestionably indicates a 

 long subaerial exposure," before the deposition of the loess. 

 In a few localities where the pre-loessial surface does not appear 

 to have suffered erosion, and where the loess therefore appears 

 to be conformable with the substratum, the junction is marked 

 by a humus-stained layer indicating an old soil. This occupies 

 the same position, relatively, as the oxidized and weathered 

 upper surface of the Orange Sands described above, and points 

 to the same conclusion as to the sequence of events. 



From the relative position of loess and Orange Sand, it is 

 evident that the latter is the older. From the stratigraphic 

 relations of the two formations, it is equally evident that the 

 deposition of the former followed that of the latter, only after 

 a, considerable interval of time. The chemical changes which 

 the older formation has suffered, strengthen the conclusion 

 drawn from the unconformity, that the interval was long. 



The main deposition of the loess seems to have taken place 

 during the second episode of the first glacial epoch. The only 

 evidence that we have thus far developed of a similar deposi- 

 tion that could be referred to the earlier episode of the first 

 glacial epoch, is found in the lower stratum of loess, separated 

 from the higher by the humus-marked and oxidized horizon, 

 referred to above, as occurring at Memphis, Forrest City, and 

 several other points on Crowley's Ridge. This lower sub- 

 division of the loess, although fairly differentiated at these 

 points, is not distinguishable at a sufficient number of points 

 to make it certain that it is the fluvial representative of the 

 first episode of the first glacial epoch." If the force of the 

 correlation of this lower division of the loess with the earliest 

 drift be set aside, it might be supposed that the Orange Sands 

 were synchronous with the first episode of this epoch. Were 

 this their age, there would have been an interval between their 

 deposition and the deposition of the loess. While this interval 

 is not believed to have been long enough, or nearly long- 

 enough, to bring about the changes which the Orange Sand 

 suffered before the loess epoch, our means of estimating time 

 may be supposed to have led to erroneous conclusions, we 

 therefore may seek the answer to the present question along 

 another line. 



* The observations recorded in the footnote on page 377, seem to make it 

 reasonably certain that the lower subdivision of the loess here referred to, is the 

 fluvial representative of the first episode of the first glacial epoch. This however 

 does not weaken the argument here adduced, although it may seem to make it 

 unnecessary. 



