AGE OF EXPOSURES OF LAFAYETTE FORMATION 251 



sippi, and in Fayette and Hardeman counties, Tennessee, there is 

 no unconformity between the Eocene Wilcox leaf beds and the 

 supposed Lafayette if the latter be restricted to the few upper feet 

 of weathered sands. 



In order that there might be no room for doubt but that the 

 Oxford exposures furnish the type-sections for the Lafayette, Dr. 

 McGee has kindly prepared the following letter covering this point, 

 at the request of Dr. T. Wayland Vaughan, geologist in charge of 

 the coastal plain investigation for the U.S. Geological Survey: 



[Copy] 



March 1, 191 1 

 My dear Doctor Vaughan: In further reply to your oral inquiry; 

 On looking up the records, I find it clear that the type locality in Lafayette 

 County, Mississippi, from which the Lafayette formation received its current 

 designation, is Oxford, the site of the state institution of learning with which 

 Dr. Hilgard was long and honorably connected; and that the type-section is 

 the exposure in the Illinois Central Railway cut at Oxford shown by Dr. 

 Hilgard in Geology and Agriculture of Mississippi (i860), p. 6, in the drawing 

 reproduced by me in "The Lafayette Formation" (Twelfth Annual Report, 

 U.S. Geological Survey, Fig. 58, p. 457). This section was in good condition 

 for examination in 1891, and was re-examined as the type-section by Dr. 

 Hilgard, the late Dr. J. M. Safford, Dr. Eugene A. Smith, Dr. Joseph A. 

 Holmes, Professor Lester F. Ward, Mr. Robert T. Hill, and myself, jointly, and 

 was still in good condition in February, 1910, when re-examined by Dr. E. N. 

 Lowe, state geologist, and myself, as the type-section cf the formation. 



Yours sincerely, 



(Signed) W J McGee 



In the exposures at Oxford the deposits are a unit with every 

 gradation from unweathered materials below to oxidized and 

 more or less ferruginous sands above. Nowhere in this region is 

 there a line of unconformity or a pebble bed to mark the supposed 

 time interval extending from the early Eocene to the Pliocene. 

 The change in color of the materials when marked at all is at 

 varying levels and is due apparently to the depth to which the 

 ferric oxide in the sands has been dehydrated. A quotation from 

 McGee's longer paper on the Lafayette will make it clear that he 

 did not recognize any unconformity between the leaf -bearing clays 

 now ascertained to be Eocene, and the overlying sands. On 

 pp. 458, 459, he says: 



