20 GEOLOGY. 



such changes have actually taken place ; for whilst the stumps 

 of trees in the salt marsh prove a subsidence of the land, and 

 an encroachment of the salt water to that point, the existence 

 of similar stumps in the tide swamps, at a depth of three or 

 four feet, equally confirms the subsidence of the land, and also 

 shows a recession of the salt water since that period. 



No division of the Tertiary is so well developed in Georgia 

 as the Eocene. This formation is bounded on the west by the 

 primary and cretaceous rocks, and it probably continues down 

 to the foot of the first terrace or sea cliff", twenty miles from the 

 ocean ; but as no fossils have been found farther east than the 

 Burr and limestone formations, it will be safer in the present 

 state of our knowledge to consider its eastern limit as extending 

 down as far as Effingham county, and passing thence in a 

 Southwest direction through the counties of Bulloch, Emanu- 

 el, and Laurens, to the lower edge of Pulaski, from which point 

 it assumes a nearly southern course, and passes through the 

 counties of Irwin and Lowndes into Florida. 



The Eocene is divided into three well defined formations, 

 the Burrstone, the orbitulite limestone, and the white lime- 

 stone. 



The Burrstone, which is the superficial formation * of this 

 group, is characterized by white, yellow and red clays, and 

 ferruginous sand, through which are irregularly interspersed 

 masses of sandstone, burrstone and siliceous rocks, generally 

 found cropping out near the tops of the hills. The fossils found 

 in it are abundant, and usually occur in a silicified state. In 

 many places they exist only in the forms of silicified casts. 

 They differ much at diflferent localities. At Atrape's quarry, 

 near Macon, a large proportion are identical with those de- 

 scribed by Conrad and Lea from the sandy strata of Claiborne 

 Bluflf; while the Burrstone of the counties of Lee, Baker and 

 Decatur, present a group of a very different character. 



The Orbitulite Limestone, which Mr. Lyell has found to lie 

 between the Burrstone and White limestone, is of a yellow, or 

 cream colour, and is almost entirely made up of orbitulites of 



* At Kinkefornia creek, near Palmyra, Lee county, a well defined section oc- 

 curs, showing the position of the Burrstone above the limestone. 



