BROWN AND YELLOW LOAM OF NORTH MISSISSIPPI 295. 



percolating calcareous waters in ramifying crevices. Specimens- 

 were taken from such crevices. 



No microscopic examination of the loam was made for com- 

 parison of its mineralogical constituents with those of the loess ;, 

 but owing to a greater degree of subsequent alteration in the 

 former it seems doubtful whether such tests when made would 

 prove entirely satisfactory. The chemical composition of the: 

 two, in their typical development, seems to differ rather in 

 degree than in kind, from the same cause, and the two pass into 

 each other by insensible gradations. 



From the foregoing it would appear that, if my observations- 

 be accurate, the Brown Loam and the Loess of this region are not 

 only homotaxial but synchronous as well. 



III. ORIGIN AND AGE OF THE LOESS LOAM. 



The Loess of the north has been distinguished as belonging" 

 to two separate epochs, and a similar twofold division of the 

 same in the south is mentioned as a probability by Chamberlin 

 and Salisbury, in an article entitled "On the Relationship of 

 Pleistocene to the pre-Pleistocene formations of the Mississippi 

 Basin, south of the limit of glaciation" [Am. Jour. Set., VoL 

 XLI). The Yellow Loam is here considered as the interfluvial 

 equivalent of the Loess, but the writer has seen nothing to suggest, 

 or which would justify, the division of the former into two or 

 more parts, separated by a time interval of greater or less dura- 

 tion. On the other hand, sedimentation generally seems to have 

 been continuous from the beginning to the close of the period 

 ■ — the first deposits, frequently composed mainly of local and 

 coarser materials, being directly followed by the finer deposits 

 which constitute the main bulk of the formation. It does not 

 follow that the Yellow Loam formation may not be of a bipartite 

 nature elsewhere ; and if it should prove universally indivisible 

 this need not antagonize the idea of a twofold division of the 

 Loess, because owing to elevation, or other causes, there may have 

 been no interstream deposit here contemporaneous with one 

 epoch or the other of the Loess, the deposition of which seems 



