392 £. W. Hilgard — Age and Origin 



are sandy ; while complete and unquestionable unconformity 

 may be exhibited in the next ridge, where the subjacent beds 

 are indurated or clayey. Similarly, apparent conformity exists 

 veiw commonly along the Mississippi river, between the upper 

 member of the Lafayette and the Loess and Port Hudson — 

 the "Columbia" of McGee. But inland the most striking 

 unconformities may be seen in abundance, proving the reverse 

 condition to be accidental. 



As regards its geological age, since it overlies the latest 

 recognized Tertiary (the Grand Gulf beds) and is in turn 

 overlain by the earliest recognized Quaternary of the region 

 (the Port Hudson), the Lafayette may, apriori, be claimed for 

 either of the two subdivisions ; being (in the " Orange Sand " 

 facies at least) entirely devoid of fossils that can with certainty 

 be claimed as its own, although containing abundance of bor- 

 rowed ones. 



Considering the conspicuously detrital nature of the materials, 

 the predominantly " fluvial " structure, and the total absence 

 of any traces of contemporary marine fossils, even close to the 

 shores of the Gulf and in materials perfectly adapted to their 

 preservation : it has seemed to me most probable that the forma- 

 tion as a whole is the outcome of the action of "fresh water in 

 the state of violent flow." At the geological level we must 

 attribute to the " Orange Sand " at least — the latest Tertiary 

 or the earliest Quaternary — the melting of the continental 

 glacier naturally suggested itself to my mind as well as to that 

 of Tuomey, with whom I discussed the subject in 1856. This 

 suggestion acquired especial force by the fact that crystalline 

 bowlders, apparently identical with those occurring in the 

 moraines of Illinois and Missouri, occur in the main axis of the 

 embayment down to the Gulf shore, where the current- velocity 

 would presumably be greatest ; while outside of that great axis 

 only the local rocks, or those not derived from any great dis- 

 tance at least, form the bulk of the gravel deposits. I was 

 thus led to consider the "Orange Sand" as the direct repre- 

 sentative and continuation southward of the "stratified drift" 

 of the Xorthwest, and have alternatively so designated it in my 

 later publications. 



Such was, summarily, the condition and aspect of the sub- 

 ject when, nearly twenty years ago, the stoppage of the Mis- 

 sissippi Geological Survey, and my removal from the South- 

 west, put an end to my personal researches in the premises. 

 The matter has passed into several text-books in that form ; 

 and the only important change made until McGee, a few years 

 ago, approached the subject from the eastward, was the recog- 

 nition by Dr. Eugene Smith of Alabama of the lower portion 

 of the Warrior gravel beds as belonging to old Cretaceous or 



