BROWN AND YELLOW LOAM OF NORTH MISSISSIPPI 2 J J 



presence of a considerable amount of hydrated peroxide of iron 

 as well as the want of proper fossils as distinctly separate it from 

 the Bluff formation of the Mississippi River 



" From the appearance of the loam stratum, even on high 

 ridges and elevated uplands, it is obvious that its deposition took 

 place, in part at least, anterior to the great denudations which 

 have produced the present surface configuration ; nevertheless, 

 its increasing thickness as we approach the immediate valley of 

 the Mississippi shows, as in the case of the Bluff formation, that 

 this great channel was already in existence. 



" On the Tombigbee, and on the lower Tallahatchie, Yalo- 

 busha, and Big Black, a similar increase in the thickness of the 

 loam stratum may be observed. But on the smaller water 

 courses this is the case only to a very limited extent, showing that, 

 although at the time of the deposition of the loam the channels 

 were already more or less impressed upon the surface and high 

 ridges existed which remained above the level of the water 

 which deposited the loam, the minor denudations which have 

 caused the present undulating surface had as yet exerted but 

 little influence. The lines of contact between the Orange Sand 

 and Loam, where the latter is evidently in situ, are generally 

 much less undulating than are those between the Orange Sand 

 and the older formations." 



A. Relation of the Brown Loam to the Lafayette. — From the 

 foregoing account, it would appear that the Brown or Yellow 

 Loam proper is a formation sui generis, deposited on a previously 

 eroded land surface in such wise as not to turn aside the larger 

 preexistent streams, and distinguished from the Lafayette only 

 by " the nature of its materials, and the entire absence of strati- 

 fication lines where it immediately overlies the latter." These 

 criteria for the discrimination of the Brown Loam and the 

 Lafayette will, of course, fail of application (i) where there 

 is no great difference in the nature of the materials of the two 

 formations, as is frequently the case, especially near their line 

 of contact, and (2) where the upper part of the Lafayette, as 

 well as the Brown Loam, is unstratified. 



