22 GUIDEBOOK OF THE WESTERN UNITED STATES 
a narrow deep-seated zone of uplift or faulting that extends across the 
country for many miles. The movements along this line, especially 
at the domes, have continued into recent times. Owing to the uplift of 
the strata the domes reveal formations which in the adjoining region 
are concealed by alluvial deposits. At the surface there is more or 
less loam resembling loess, 10 feet or more thick, and in many places 
where this has been removed by erosion older gravel (Citronelle, 
p. 19) is exposed. On Avery Island there are small exposures of 
sandstone, clay, and lignite which may be of Pliocene or Miocene age. 
Sa Ae oe 
Recent 
Pleistocene 
Pliocene 
Miocene 
an 
Oligocene (?) 
Jackson (Eocene) 
Claiborne 
(Eocene) 
; Wilcox 
(Eocene) 
Midway (Eocene) 
Upper Cretaceous 
(Lower Cretaceous) 
alt,age? 
FIGURE 1.—Hypothetical section of salt dome at Avery Island, La. 
By ’. Howe 
In places here the beds dip 44°. The lignite, which is 18 feet thick, 
may have economic value. 
At Jefferson Island there is a small mound only 75 feet high, but it 
has been found by recent boring that the area of doming is consider- 
ably larger, the salt core extending under Lake Peigneur; the depres- 
sion in which the lake lies may be due to subsidence caused by the 
removal of salt by underground solution. 
There have been several theories as to the origin of the numerous 
salt domes in the Coastal Plain of Louisiana and Texas, but most 
geologists regard them as due to the flow of the relatively plastic salt 
from a deep-seated stratum, to relieve stress in the earth’s crust. 
The salt body has forced its way through the overlying sand and clay 
