278 T. O. MABRY 



Wherever the loam attains a thickness of 10 or 12 feet — and 

 it is rarely thinner than this for any considerable distance — it 

 is usually not difficult to identify it, especially its upper portion, 

 but, as Hilgard has long ago pointed out, this formation is fre- 

 quently so modified by underlying terranes as to render its delim- 

 itation in those places a matter of great difficulty, if not impos- 

 sible. For instance, locally the characteristic loam may be 

 replaced by sand variously colored ; and when all traces of 

 stratification, if they ever existed, have become obliterated 

 through the action of percolating chalybeate waters, which both 

 color and cement the sand grains, and when this red, sandy 

 phase of the "Brown Loam" or "Yellow Loam" rests directly 

 upon similar sands of the Lafayette — whence the former have 

 generally been derived — it frequently becomes a matter of 

 impossibility to draw any certain line between the two. This is 

 often the case in the "red lands " of the Pontotoc Ridge and its 

 northward continuation, the " Buncombe Hills." However, judg- 

 ing from an exposure near the depot in the town of Pontotoc, 

 and from numerous other sections on the ridge, both the brown 

 loam and the Lafayette seem to be represented in the Pontotoc 

 Ridge ; but as we shall presently see, the Lafayette is frequently 

 absent in northeast Mississippi, the Brown Loam resting directly 

 upon still older formations. 



A section in the cut on the Illinois Central Railroad just 

 south of the depot at Oxford shows typical loam at the top, 

 grading into rotten or friable clay, which, becoming more sandy 

 below, passes insensibly into a semi-indurate, massive red sand- 

 stone. The base of the section here shows nicely stratified 

 sands and clays, presumably of Lafayette age, though possibly 

 later, but no definite line can be drawn between the two forma- 

 tions at this exact point. 



While we cannot always with certainty determine, in the 

 field, the limits of the two formations, and while there are to 

 be found places of seeming local conformity, which we should 

 naturally expect, still the two can generally be separated with- 

 out difficulty, because, when typically developed, the two forma- 



