JACKSON FORMATION". 33 
LISBON BEDS. 
The uppermost division of the Claiborne is a series of elays and sands, which Hilgard 
called "calcareous Claiborne." The formation is estimated to be 150 feet thick in Alabama, 
where it is composed of calcareous sands and laminated and lignitic clays. There is one 
horizon in Alabama in which a distinguishing fauna occurs. This is a bed of yellowish 
ferruginous sand 15 to 17 feet thick, containing numerous species of beautifully preserved 
Claiborne fossils. A large number of the fossils in the Lisbon beds range through the over- 
lying Jackson and Vicksburg formations. 
The fossiliferous horizon above mentioned has been described by Hilgard as occurring on 
Falling Creek, near Quitman, Clarke County, Miss., and on Suanlovey Creek, west of Enter- 
prise. L. C. Johnson has also collected fossils from the same bed at the Wautubbee cut, 
southwest of Enterprise. Here it is 17 feet thick and is the best collecting bed of the Clai- 
borne so far found in Mississippi. 
The same bed outcrops again 4 miles northwest of Newton, in Newton County. The 
material in which the fossils occur is a blue calcareous sandy marl. The bed here is much 
thinner than at Wautubbee. Frank Burns, of the Smithsonian Institution, has made a 
large collection of fossils from this place, as well as from numerous other places west of 
Hickory and along the road between Hickory and Quitman. The fossils have all been 
examined by Dr. W. H. Dall and referred by him to the Lisbon beds of the Claiborne. Near 
Hickory and southward to Quitman most of the fossils occur in a sandy " soapstone " or clay. 
One mile south of Enterprise, on Chickasawhay River, is a bed of Scutella lyelli, which has 
become cemented into a hard rock, as reported by Mr. Burns. The Scutella bed overlies a 
bed of fine ash-colored marl, which contains a large amount of greensand, but is devoid of 
fossils at this place. 
In the railroad cutl^ miles west of Decatur Claiborne fossils occur in a bed of dark-blue 
glauconitic clay marl. This is doubtless near the base of the formation, as the buhrstone 
outcrops about 4 miles northwest of Decatur. 
JACKSON FORMATION. 
In Alabama the Jackson and the succeeding formation, the Vicksburg, have been classed 
together under the name of St. Stephens. In Mississippi, however, the two formations 
can usually be separated quite readily and will be treated as two distinct formations. 
The essential materials of the Jackson group are gray calcareous clay marls and bluish 
lignitic clays, with greensand and gray siliceous sands. From a lithologic standpoint there 
is very little difference between the calcareous clays and marls of the upper Claiborne and 
those of the lower Jackson. In general the color of the clays becomes lighter in the Jack- 
son, with possibly a less amount of lignitic material. So far, however, the principal reason 
for keeping the two formations separate is based on paleontologic evidence. In some locali- 
ties where fossils have been collected, the so-called Claiborne fossils were so evenly distrib- 
uted with those of Jackson age that it has been difficult to say in which formation the beds 
belong. There is need of a more comprehensive study of the stratigraphy in connection 
with the fossils in order to draw the line between the two formations correctly. This line as 
mapped in Mississippi is, therefore, only approximately correct. The upper ferruginous 
sandy marl containing Claiborne fossils has been seen in but few places in the State. Smith, a 
in speaking of the distinction of Claiborne and Jackson rocks, says: 
The rocks of the Claiborne group are distinguished from those of the white limestone (Jackson and 
Vicksburg of Mississippi) by the presence of glauconite in large proportion, and this Scutella bed is the 
first of the ferruginous beds of the Tertiary. We are undecided whether this Scutella bed should go 
with the white limestone or with the Claiborne, since the fossil is found in both formations. 
Only a few feet below this Scutella bed are the Claiborne fossiliferous sands, so that even 
where the formations have been best studied there seems to be a gradation in both the 
a Coastal Plain of Alabama, p. 111. 
Bull. 283—06 3 
