46 PROCEEDINGS OF THE ACADEMY OF [1887. 



equivalent Tertiary strata rest upon the Ripley Group in Missis- 

 sippi; but in Texas the actual contact seems not yet to have been 

 seen by a comj^etent observer. The faunal difference also, between 

 the Navarro and the Lignite Beds, plainly indicate a change in 

 physical conditions, and also a chronological break of some 

 extent. The break, however, may have been only a brief one. 



On the other hand, the strata of the Fox Hills Group in the 

 region of the Rio Grande are directly overlaid by those of the 

 Laramie Group, the two formations so blending together that no 

 sharply defined plane of demarkation between them can be 

 recognized. Thus we find the stratigraphical series in that 

 western region to be an unbroken one up to the top of the 

 Laramie Group; while the eastern series is broken at the top 

 of the Navarro Beds. We are therefore still in doubt as to the 

 true stratigraphical relation of the Laramie Group with the 

 Eocene Tertiary of the Gulf region. If that relation is ever 

 discovered, it now seems certain that we shall find it in the 

 southwestern part of Texas, or the adjacent part of Mexico. 



The Dakota Grouji of the western and upper Missouri sections 

 rests directly upon Jurassic strata, which in turn rest upon a 

 series known as the "Red Beds," and usually regarded as of 

 Triassic age. Those Red Beds are there found to rest upon the 

 Carboniferous, or upon older j^aleozoic rocks. No equivalent of 

 the Jurassic strata referred to have been recognized in connec- 

 tion with the Texas Cretaceous section as given in this article; 

 and they seem to have entirely thinned out before reaching the 

 region of Central Texas. In that region, the strata next under- 

 lying the Comanche series are clearly either those of the 

 Carboniferous, or of the Red Beds. The latter are not known 

 to exist to the eastward of the Carboniferous area of Northern 

 Central Texas, but they reach considerable thickness upon the 

 western side of that area, Avhere they are usually known as the 

 Gypsum formation. 



It appears from the investigations upon which this article is 

 based that certain of the members of the Texas Cretaceous 

 section have not heretofore been recognized, and that the true 

 order of superposition of the formations has been misunderstood, 

 the theoretical section of Marcou' being more nearly correct than 

 any heretofore published. It also appears that while the lower 



iProc Boston Soc. Nat. History, Vol. VIII, p. 93. 



