Gulf Pine Barren-Strand District. 445 
of the dunes associated with Opuntia pes-corvi and Siphonychia erecta. The 
dead tops of Pinus clausa and buried trunks of Yucca aloifolia covered by the 
drifting sand heighten the impression of aridity. In Mississippi and Louisiana 
the wandering dunes are frequently captured by thickets of /er and Myrica 
gale. Other dunes show on their windward slopes a vegetation of annuals and 
perennials composed chiefly of /va zmbricata, Serenoa serrulata with occasional 
clumps of Unzola and Siphonychia. These dunes are in rapid motion and have 
left behind them a “graveyard” of dead pines. 
The crests of the barrier islands along the Gulf coast of Texas, according 
to the researches of BRAY') are composed of unstable sand dunes. In front 
of this crest the compact beach sands slope to the surf line, while on the 
shore side, the islands slope away to the marsh tide flats or lagoons, or a 
succession of older dunes tenanted by salt plants, prairie grasses, Yucca Tre- 
culeana, Prosopis juliflora, Celtis occidentalis. On Brazos Island, the unstable 
dune crests are held by Umiola paniculata, so that as the sand blows away 
hay-cock dunes are formed. 
Sand Plain Formation. Physiographically the sand plain consists of (1) 
shallow depressions generally wet; (2) low dunes; (3) level stretches of sand. 
The shallow basins are tenanted by a species of Hydrocotyle and Mollugo 
verticillata. The dunes are formed by Panicum repens and halophilum, Iva, 
Serenoa, while extending between the elevations and depressions are plants 
which do not produce a network of roots and stems, viz., Scirpus, Oyperus 
Diodia, Syntherisma, Cenchrus. Open grass plains exist in these places 
characterized by a plant covering of a large number of herbaceous species of 
low stature with such grasses as Chaetochloa magna, Uniola paniculata and 
certain slender vines. Another type of sand plain is the forest-covered 
area found only on the larger islands of the Mississippi Sound. Broadly 
speaking the whole area is covered by a forest of pines of two species, Pinus 
palustris (= P. australis), P. Taeda with Sabal Adansonii and Serenoa as pro- 
minent elements in the undergrowth. Old long captured dunes are occupied 
by Quercus geminata and O. virginiana whose trunks are clothed by Ra- 
malina 
Shell Strand Formation. "On the shore of the sea of the mainland and smaller islands 
along the banks of the bayous are heaps of Basine shells 6 to 15 feet and over in height the 
cover these heaps of shells together with dense copses of Aa pavia, er caro 
e West i 
c 
posed situations it becomes low and stunted. Thurberia arkansana is typie of these shell heaps 
from South Carolina to Texas. Evolvulus alsinoides widely distributed in the tropies has been 
observed on the shell deposits of Dauphin Islan 
Salt Marsh Formation. The low islets Bug the Alabama coast and elsewhere 
along the Gulf coast are bare of tree growth and their soil is soaked by the 
ı) Distribution and Adaptation of the Vegetation of Texas. Bulletin University of Texas 
No. 82 Scientific Series No. 10, 1906: 106. 
