BROWN AND YELLOW LOAM OF NORTH MISSLSSLPPL 283 



3. The degree of oxidation and attendant phenomena pro- 

 duced in the Lafayette prior to the deposition of the Yellow 

 Loam, by atmospheric and aqueous agencies, likewise tell the 

 story of a considerable interval of chemical as well as mechan- 

 ical erosion between the periods represented by these two forma- 

 mations. (See Am. Jour. Sci., Vol. XLI, p. 370.) 



4. The facts already presented show conclusively that a 

 long period of erosion intervened between the time of deposition 

 of the Lafayette and that of the Yellow Loam. Over most of 

 the area embraced within the scope of this paper the Lafayette 

 seems to be essentially a continuous deposit, with the Yellow 

 Loam resting directly and unconformably upon it, although its 

 irregular stratification and the alternating layers of coarser and 

 finer material indicate varying local conditions such as would 

 result if the formation were deposited in the manner supposed 

 by Hilgard. 



McGee finds evidence in some localities of a twofold and 

 even of a threefold division of the Lafayette, the divisions being 

 separated by "pseudo-unconformities," which, according to him, 

 represent only local shifting of currents, and consequent change 

 in deposition, and do not mark the limits of distinct episodes. 

 {12th Ann. Rep. U. S. Geol. Surv., pp. 453-456, and elsewhere.) 



But sections observed by the writer have caused him to 

 doubt the unity of the Lafayette, as now defined in its type 

 locality, and to raise the question whether the uppermost mem- 

 ber of the Lafayette may not represent a distinct formation. 



Occasionally there is found a stratum of clay and sand, or 

 of clay alone, intercalated between the main bulk of the Lafayette 

 and the Yellow Loam, and sharply separated from both by irreg- 

 ular or billowy erosion lines. This deposit is usually only a few 

 feet in thickness, and consists, [a) of compactly bedded pipe 

 clay, (&) of interlaminated clay and sand (the different layers 

 sometimes quite thin, sometimes several inches thick) , or (<:) of 

 a heterogeneous, unsorted mixture of sand and clay bowlders of 

 various shapes and dimensions, resembling very much in physi- 

 cal characteristics, the unsorted till of the North. 



