SOUTHERN PACIFIC LINES 
19 
Formations of Quaternary and Tertiary age underlying southern Louisiana 
Age Formation Character Boon or 
Beaumont clay. Clay and sand. 
Pleistocene. 1,500+- 
Lissie gravel Sand and gravel. 
U on fi rmity- 
Pliocene. Citronelle formation. oi ~ieess yellow and red sand and 50-400-+- 
U neonform mity- 
Paseagonla clay. a neon: blue-green and gray | 959 1 400(7) 
nf — 
Miocene. Hattiesburg clay. Ni or nt a eray clay, thin 300-350 
Nonmarine; gray sand, sandstone, fine 600-800 
Catahoula sandstone. conglomerate, clay 
Jackson formation. — gray sand and dark calcareous 100-600 
Eocene, 
Palustrine; gypsiferous sand and clay 
Cockfield formation. with lignite. 400-800 
Some recent estimates suggest that in the southern part of the area 
the Pliocene and later beds are 4,000 feet thick, the Miocene 4,000 
feet, the underlying Tertiary more than 10,000 feet, and the Creta- 
ceous possibly as much as 8,000 feet. This great succession of sedi- 
ments indicates that the region was under water for a long time, during 
which a vast amount of material derived from the land was deposited. 
During this deposition the basin kept sinking much of the time, and 
doubtless the total amount of subsidence was fully 5 miles. There 
were also intervals of uplift when the land was above the water, a fact 
indicated by unconformities between most of the formations above 
listed. There is evidence that the region is still subsiding, for a few 
centuries ago cypress swamps were much more extensive than at 
present, as shown by the dead cypress on Cypremort Point and by the 
stumps of cypress in Weeks Bay, exposed at very low tide 
Southern Louisiana has had a somewhat complex fluviatile history, 
some of it decipherable from the resulting configuration or the distribu- 
tion of deposits. Near New Iberia there are small areas of character- 
istic Red River deposits, which indicate that at no distant date the 
Red River drained south for a short time through Bayou “Teche. 
Deposits of the latter stream overlying the low terrace plain southeast 
of New Iberia indicate that for a while this bayou overflowed its banks 
in the wide gap east of New Iberia and reached the Gulf between 
Avery Island and Weeks Island. (Howe.) 
