H kk Y ^ne£y D ] GEOLOGY OF EASTERN DIVISION. 19 
PROSPECTING FOR PETROLEUM. 
Prospecting for petroleum in this region is not being carried on very 
vigorously. For a number of years petroleum has been obtained 
from a well in the northwestern part of Starr County, but the quan- 
tity is so small that the oil is usually drawn up by an ordinary water 
bucket and is sold to local consumers for medical purposes. 
A well has recently been drilled at Piedras Pintas, near Benavides, 
on the Mexican National Railroad, in Duval County, to a depth of 
1,200 feet. Small quantities of oil were found at various depths, but 
not enough to justify further developments, and the work has been 
abandoned. This well is in the sandstone region near the northern 
margin of the Coastal Plain and has an elevation above sea level of 
400 feet. 
Another well, drilled on the La Parra ranch, in the northern portion 
of Cameron, to a depth of 1,500 feet, has been abandoned. The con- 
tractor states that he drilled through clay and sand the whole depth. 
GEOLOGY OF THE EASTERN DIVISION. 
GENERAL SECTION. 
The general section of the Texas Tertiary formations shows consid- 
erable variation in the character and thickness of the various beds, 
and there are such extensive erosions and overlaps that it is somewhat 
difficult to say whether some of the beds actually occur at a stated 
locality or at what depth the rocks belonging to the given stage may 
be found. The beds thicken and thin rapidly, and change frequently 
from soft sand to indurated sandstone, while the clay bodies all appear 
to have a somewhat wavy or lenticular form. 
In the following section the maximum thicknesses have been given, 
as it has been thought better to place before the w r ell driller the 
utmost thickness of any of the beds he may be expected to go 
through. But, as will be pointed out later, this section will be mate- 
rially modified as to the thicknesses by the location of the well. 
The section down to the Eocene is constructed chiefly from well 
records. It has been thought best, for clearness of presentation, to 
give a generalized description of the various formations which make 
up the Coastal Plain, to be followed by the detailed sections and local 
descriptions on which it is based. 
General section of eastern division of Texas-Louisiana Gulf Coastal Plain. 
Thickness 
in feet. 
1. Recent: Coastal marshes consisting chiefly of sea flats subject to 
overflow at extremely high tides, swamps and partly submerged 
lands, and the bottom lands along the rivers. The life represented 
by recent shells, such as Rangia cuneata and Ostrea. Beds of 
these shells occur along the rivers and at many of the smaller 
lakes in this region 5 to 25 
