600 D. W. LANGDON, JR. — CRETACEOUS AND TERTIARY STRATA. 



The division of the middle Tertiary into calcareous and silicious Claiborne 

 seems more appropriate on the Chattahoochee than classification as Claiborne 

 and Buhrstone, since the latter has become so closely related to the former 

 in abundance and character of fossils that any division whatever is, in this 

 region, purely arbitrary. 



The White Limestone becomes a little thicker on the Chattahoochee, but 

 loses its distinctiveness as Jackson and Vicksburg and may well be included 

 under one head. 



Apart from and pari passu mth thefaunal changes which have been indi- 

 cated, it will be seen from the accompanying sections that there is a thinning 

 out of the aggregate strata to the extent of some 500 feet in the Tertiary and 

 1,100 feet in the Cretaceous. 



General Section Exposed on the Chattahoochee River. 



The successive beds exposed on the Chattahoochee from Columbus, Geor- 

 gia, to Alum bluff are as shown in the following table, in which the order 

 of enumeration is that of historical succession, or the inverse of the strati- 

 graphic succession. They are illustrated graphically, in connection with the 

 Alabama and Tombigbee exposures, in plate 23. 



Feet. 

 l^Light green, highly micaceous sand, resembling weathered schist; but for 



occasional water- worn quartz pebbles might be mistaken for schist 3 



2 — Hard clay stained by ferruginous matter ; breaks with conchoidal fracture. 1 



3— Hard, white, coarse-grained sand, held together by white clay 15 



4 — Eed and gray variegated sandy clay (typical Tuscaloosa) ; shows at water's 



edge, mouth of Bull creek, Georgia 6 



5 — Strongly cross-bedded coarse sand and pebbles with some few fragments of 

 schist and just enough white clay to hold the mass together. The quartz- 

 ose pebbles are all well water- worn, while the softer bits of schist are but 

 slightly abraded. This stratum varies in color from white to lemon 

 yellow and in places green, while the upper part becomes mottled purple 

 and yellow. This last phase is most strongly developed at Thomas' bluff, 



Georgia, due east of Fort Mitchell, Alabama 40 



6 — Dark-gray calcareous sand, pyritous and containing nodular masses 6 to 12 

 inches in diameter with calcite nuclei. These nodules are arranged in 

 strata about two feet apart and terminate in an indurated stratum about 

 12 inches thick. Small fragments of lignite are scattered about through 

 this stratum, and oneor two large masses filled with calcified teredos were 

 found. The only other fossils seen were an Ayiomia and an Exogyra, 

 probably the young of E. costata^ Say. The fossils are all poorh'- pre- 

 served. Dip at this point, 40 feet to the mile southward 15 



7 — Gray sands of the same nature as the preceding, only no nodules were seen, 

 and the shells increase in quantity, particularly in the lower part. The 

 upper part of this stratum becomes more argillaceous and contains many 

 fossil casts, mainly lamellibranchs ; causes landslides in the banks like 

 the Black Bluff clays, which they resemble somewhat physically. These 

 sandy clays give rise to Uchee shoals 100 



