39i E. W. Hilgard — Age and Origin 



ment of the Cretaceous and Tertiary formations in the Missis- 

 sippi embayment. 



I think that many if not most of the differences which have 

 arisen between McGee and myself in the interpretation of the 

 jmenomena of the Lafayette formation have been due to the 

 different starting points. McGee, coming from the Atlantic 

 coast, naturally carried the views acquired there into the terri- 

 tory where, I am inclined to think, a materially different mode 

 of development has occurred ; as would naturally be expected 

 in so critical a region. The joint reconnoissance made last 

 summer has, I think, materially diminished these differences 

 of views ; and the extension of this reconnoissance around the 

 Gulf shore into Mexico by himself and party will, I hope, 

 prove the fruitful first step toward the final unraveling of the 

 complex questions which, alone, I was powerless to solve. 



Broadly speaking, the difference of views referred to may 

 be summarized in this, that while McGee regards the whole of 

 the Lafayette formation as having been formed under a condi- 

 tion of continental depression and marine submergence, I have 

 on the contrary, referred the origin of the " Orange Sand " of 

 the Embayment to a period of elevation, and the deposition of 

 its materials essentially to fresh water in the form of broad and 

 shallow floods coming in from the northward and practically 

 devoid of organic life of which the remains would be likely to 

 be preserved. All are, however, agreed that the deposition, 

 by whatever agency, was succeeded by a relatively long period of 

 elevation or at least emergence, during which subaerial exposure 

 brought about both the surface sculpture and the condition of 

 complete peroxidation, and leaching of all water-soluble ingre- 

 dients, that is so prominent and essential a feature of the 

 " Orange Sand " phase of the formation. For within its beds,, 

 nothing that is capable of further oxidation or water-solution 

 remains, so that agriculturally the formation, alone, is about as 

 barren as can well be. 



That the paludal nature of the overlying Port Hudson beds, 

 as well as the fluvial and calcareous nature of the Loess, neces- 

 sitates the assumption of a subsequent re-depression, need 

 hardly be more than mentioned. The extent of this oscillation 

 I will presently consider. 



It would seem from the character of the formation as 

 observed on the Atlantic coast, that the evidence of long emer- 

 sion and subaerial exposure is not so cogent there. Certainly 

 the leaching process, as well as that of ferrugination, has not 

 been carried so far as is the case in the Embayment, since ac- 

 cording to McGee, the gravels still contain rare calcareous peb- 

 bles; of which, as before stated, not a trace remains in the 

 " Orange Sand," although limestone formations are plentiful 



