84 TERTIARY SYSTEM. 



185. The marine Eocene, commencing in New Jersey with a thickness of 37 

 feet, and exposing only a narrow surface area, crosses Maryland by way of Fort 

 Washington ; Virginia, by way of Fredericksburg, Richmond, and Petersburg ; 

 North Carolina, by way of Newbern and Wilmington ; South Carolina, by way of 

 Charleston and Shell Bluff, on the Savannah River ; Georgia, by way of Milledge- 

 ville ; Alabama, by way of Claiborne ; and Mississippi, by way of Jackson and Vicks- 

 burg. In South Carolina it consists of loose sand, clay, gravel, sandstone, lime- 

 stone, and marl, covers a large area, and has a thickness of 1,100 feet. It is 

 divided into the Buhrstone Group, Santee beds, and Ashley and Cooper beds. It is 

 exposed in Florida, and reaches up into Tennessee, where it is called the Porter's 

 Creek Group. Conrad subdivided it in Alabama and Mississippi, where it has a 

 thickness of about 900 feet, into the Claiborne Group, Jackson Group, St. Stephen's 

 Group, and Vicksburg Group. It crosses Louisiana, appears in Arkansas, and 

 offers numerous exposures in Texas, Mexico, and California. It is extremely fossil- 

 iferous at many places, and nowhere conformable with the underlying rocks. 



186. The gradual elevation of the western ranges of mountains through 

 Cretaceous and Tertiary time, the formation of bays and arras of the sea, and lakes 

 which have drained themselves in continuing succession, have linked the Tertiary 

 with the Cretaceous, and bound the Eocene, Miocene, Pliocene, and Post-pliocene 

 with the present, almost as one connected age. In these lake regions the Eocene 

 is divided into the Wahsatch Group, Green River Group, Bridger Group, and 

 Brown's Park Group, and there are numerous synonyms for each one of them. The 

 Wahsatch is characterized by its brick-red color, and has a thickness of 8,000 feet; 

 the Green River Group is quite fossiliferous, and has a thickness of 7,500 feet; 

 the Bridger Group rests conformably on the Green River, consists of Bad Land 

 sandstones, limestones, shells, and marls, and has a thickness of 2,000 feet ; and the 

 Brown's Park Group has a thickness of 2,500 feet. The combined thickness of the 

 Eocene in the Western Territories is therefore 20,000 feet. 



187. The marine Miocene beginning at Martha's Vineyard, though it may 

 exist as far north as Maine, crosses New Jersey through Cumberland County, and 

 forms a border upon the east and south of the Eocene exposure a large part of the 

 way to the Mississippi River, and west across Louisiana, Texas, and Mexico. It is 

 not conformable with the Eocene, and in some parts does not intervene between it 

 and later deposits. It has its greatest thickness in California, where it exceeds 3,000 

 feet. The Coast Range of mountains is composed in large part of strata of this 

 age, and hence its elevation has been since the Miocene period. It is highly fossil- 

 iferous, and the shells generally belong to living genera, and many of the species still 

 survive in the waters bordering the adjacent coast, thus indicating no material change 

 in the climate since that period. The Miocene lake deposits, like the Eocene, cover 

 great extensions of Territory and reach an enormous thickness. In Nebraska it has 

 been divided into the Wind River Group, which has a thickness of 2,000 feet, and 

 the White River Group, which has a thickness of 1,000 feet. On the divide between 

 the Arkansas and South Platte, where the thickness is from 1,500 to 2,000 feet, it 

 is called the Monument Creek Group, and in Oregon it is called the Truckee Group. 



188. The marine Pliocene strata are found in Maryland, superimposed upon 

 the Miocene, in South Carolina, upon the Eocene, and generally forming a narrow 

 border at the east of these outcrops on the Atlantic coast, and a wider border on 



