E. W. Hilgard — Lafayette Formation, etc. 389 



Aet. XLYIII. — The Age and Origin of the Lafayette For- 

 mation ; by Eugene W. Hilgard. 



The interest so widely felt in the Lafayette formation since 

 its great extension northward has been definitely established 

 and its details in that region studied by Mr. W. J. McGee, and 

 described in other special communications on the subject which 

 have reached me, suggests the timeliness of a summary presen- 

 tation of my views, as shaped under the light of a fuller view 

 of the whole formation and a review of the matter in the Mis- 

 sissippi Embayment during the past summer, by a party of 

 geologists. This party included, besides Mr. McGee and my- 

 self, Professors Safford of Tennessee, Smith of Alabama, 

 Holmes of North Carolina, and Lester F. Ward and R. T. Hill 

 of the IT. S. Geol. Survey. 



As the publications containing the record and discussion of 

 my former observations (in which the formation carries the 

 name of " Orange Sand," now dropped by agreement) are 

 difficult of access after the lapse of from twenty to over thirty 

 years, it may be necessary to recapitulate, summarily, the main 

 points as then presented, in order to render the later discussion 

 intelligible to all interested. 



The eastern outline of what I have called the " Orange 

 Sand Delta " extends from a point near Cairo, through western 

 Kentucky and Tennessee, nearly through the northeast corner 

 of Mississippi into Alabama ; whence, as I then ascertained 

 from the descriptions of Tuomey, and by correspondence with 

 Dr. Joseph LeConte, it passes eastward around the Appa- 

 lachian highlands into the Carolinas and thence north to 

 Yirginia and Maryland. On the west, I traced, the formation 

 by D. D. Owen's descriptions through Arkansas, and person- 

 ally through Louisiana and across the Sabine into Texas. 



Within the limits given, say between the Warrior river on 

 the east and the Sabine on the west, and excepting the areas 

 occupied by the Cretaceous prairies, the (Tertiary) " Flatwoods," 

 the Loess, and the Mississippi bottom, the formation as a rule 

 lies at or near the surface of the country, most frequently 

 covered by a few (three to ten) feet of brown or yellow loam 

 of much later date, since it also overlies the Loess. The 

 characteristic concretionary ferruginous sandstone of the for- 

 mation (replaced occasionally by a white siliceous sandstone or 

 chert) caps nearly all the higher ridges, the crests of which it 

 has protected from degradation, and usually forms the upper 

 portion, or sometimes the entire body of such ridges ; showing, 

 by their alternation with others bearing only a thin cap of the 



Am. Jour. Sci.— Third Series, Vol. XLIII, No. 25?.— Mat, 1892. 

 26 



