200 GEOLOGY. 



and dip seaward, disappearing beneath younger formations. As along 

 the Atlantic coast, the Eocene sediments seem to have been derived 

 largely from the Cretaceous; but this is not true of all parts of the sys- 

 tem, for about the lower Mississippi, much of the Lower Eocene is 

 lignitic, while the Upper Eocene (in Mississippi and Alabama) is com- 

 posed largely of limestone. A great bay or estuary appears to have 

 occupied the site of the lower part of the Mississippi as far north as 

 the mouth of the Ohio, and in this embayment the deposits extend 

 much farther north than elsewhere. The Lower Eocene (Lignitic 

 formation) extends farther north than the later beds. 



Western Gulf region. — The Texas Eocene, 1 which sometimes appears 

 to be conformable with the Cretaceous, is composed chiefly of shallow- 

 water marine deposits; but lignite, and gypsiferous and saliferous 

 sediments recur at various horizons, showing the recurrence of ter- 

 restrial and non-marine conditions within the general area of depo- 

 sition. Iron ore and silicified wood are of common occurrence in con- 

 nection with the lignite. There are numerous local unconformities in 

 the system, suggesting recurrent changes in the conditions and areas 

 of sedimentation. The Lower and Middle series are represented, and 

 probably the Upper, though there is difference of opinion as to the 

 upper limit of the system in this region. 2 The system attains a thick- 

 ness of several hundred (800 at least) feet. Various names are applied 

 to different parts of the system in different parts of the State. The 

 fossils are such as to suggest that shallow-water marine life was able to 

 find its way from the Guff to the Pacific, and vice versa, during this 

 period. 



The Eocene of Texas and Louisiana is continued northward into 

 Arkansas, where the Lower and Middle divisions, and perhaps the 

 Upper, are found. 3 



The Pacific Coast. 



The changes which marked the close of the Mesozoic era resulted 

 in the exclusion of the sea from most of that part of the present land 



1 Dumble, Jour, of Geol., Vol. II. See also Reports of the Texas Geological Sur- 

 rey, and the Austin and Uvalde folios, U. S. Geol. Surv. 



* 2 Texas Geol. Surv.; Hayes and Kennedy. Bull. 212, U. S. Geol. Surv., pp. 22, 

 23; Smith and Aldrich. Science, New Series, Vol. 16, pp. 836-9, and Vol. 18, p. 26; 

 Dall, Science, Vol. 16, p. 946 and 18th Ann. Rept,, Pt, II, U. S. Geol. Surv. 



3 Harris, Arkansas Geol. Surv., Vol. II, 1892. 



