62 OIL FIELDS OF TEXAS-LOUISIANA COASTAL PLAIN, [bull. 212. 
GRAVELS. 
Lying at the base of the Columbia beds, and apparently more inti- 
mately connected with them than with the underlying red and brown 
sands, there generally occurs a heavy bed of beach gravel. This 
gravel covers the whole of the territory occupied by the underlying 
red clays and sands, and in many places overlaps other underlying 
deposits as far north as the outcrop of the Yegua clays. The gravel 
is irregularly deposited, being found in heavy deposits at some local- 
ities and in very small quantities at others, without any apparent 
cause for the irregularity. Along the northern border of the forma- 
tion there appeal's an intermingling of the sands and pebbles, but 
within a very short distance southward the gravels have generally 
disappeared from the sand beds. 
The pebbles forming these beds include clear and milky quartz, 
agate, jasper, carnelian, and some chalcedony, with considerable 
quantities of gra} r -blue and black chert, and some ciystalline rock. 
The chert and some of the other pebbles have retained their angular- 
ity to a considerable extent, which would lead to the conclusion that 
they have not traveled any great distance. Most of the others are 
rounded and waterworn. AVhile in some places the pebbles occur 
mixed with sand or in an unconsolidated gravelly condition through- 
out the greater portion of the field, as especially shown in the records 
of the deeper well drillings, the pebbles are cemented by a white 
calcareous mat rix and form a conglomerate of variable hardness. 
The actual areal extent of these gravels and conglomerates is not 
known with any certainty, but they appear to be coextensive with 
the Columbia beds and with them to pass under the overlying clays. 
The}' are found in one or the other form in every well sufficiently 
deep throughout the whole coast country from the Mississippi west- 
ward to the Guadalupe River, and probabl3 T even farther west. 
In almost every well drilled or dug down to them these gravels are 
shown to lie between the two sands. In thickness they vary from 10 
to 80 feet; their greatest thickness as well as greatest areal develop- 
ment is toward the eastern or Mississippi end, and they gradu- 
ally thin out toward the west and southwest. They also lie at a 
much greater depth in the western than in the eastern portion of the 
Coastal Plain. Throughout the parishes of St. Marys, New Iberia, 
and St. Martins they lie at depths ranging from 94 feet at Arise la 
Butte to 150 feet 3 miles southwest of Jeanerette, a where they have a 
thickness of 64 to DO feet. In Arcadia and Vermilion the} 7 have 
thicknesses of from 41 to 80 feet, and lie at depths ranging from 140 
to 170 feet in Arcadia Parish and from 100 to 170 feet in Vermilion. 
In this region it is evident from Mr. Clendenning's sections, as well 
as those made by Mr. Hager, & that these gravels underlie the clays 
« W. W. Clendenning, G-eol. and Agric. of Louisiana, Part III, 1896, p. 243. 
b Communicated to writer by Mr. Lee Hager. 
