SOUTHERN PACIFIC LINES 61 
which is 700 feet thick in this vicinity. The relations are shown in 
Figure 5. 
A few miles southwest of Luling is the Darst Creek oil field, dis- 
covered in 1929 and also drawing from the Edwards lintiekouc. the 
depth of which in the first well was 2,605 feet. The oil here, as in 
the other fields near by, is believed to have migrated up the dip and 
become trapped in the upper porous member of the Edwards lime- 
stone, here sealed off by a fault that has brought it up against imper- 
vious strata. This fault is estimated to have a displacement of about 
525 feet. It trends northeast, parallel to the Luling and other faults. 
(Brucks.) The production in 1930 ranged from about 15,000 to 
36,452 barrels a day and amounted to 11,424,000 barrels for the 
year from about 253 wells. The productive area is about 4% miles 
long and in places 3,500 feet wide, covering about 1,500 acres. 
In the Luling field, which is Honaky 8 miles long aba half a mile wide, 
the oil occurs in the upper part of the Edwards limestone, at an aver- 
age depth of about 2,100 feet. This field reached a Beak production 
of about 11,134,000 barrels4 in 1924, with 567 wells, but in 1928 it had 
diminished to half that amount, aiid in 1930 it yielded 3,692,000 
barrels, or about 10,000 barrels a day. The total production to the 
end of 1930 was about 50,000,000 barrels. The oil has a gravity of 
26° to 29° Baumé.*! 
Some interesting data have been obtained from borings in the 
Luling field as to underground temperatures. In general the temper- 
© Below the Indio are 280 feet or 
more of tough clays and glauconitic 
sands of the Midway group (basal 
Tertiary), which lie unconformably on 
Navarro clay, here about 500 feet 
thick and containing some thin beds of 
sandstone. Next below are about 500 
feet of Taylor clays and chalky clays, 
which extend to the Austin chalk, 228 
feet thick, underlain by the Eagle Ford 
shale, 30 feet; B i 
limestone, 60 to 110 feet, lying on the 
Edwards limestone. (MeCullum and 
Cunningham.) See also table, p. 65. 
*' According to Brucks the structure, 
which is similar to that in the Salt Flat 
and Darst Creek fields, shows a faulted 
monoclinal block with northeast trend. 
The upthrow is about 450 feet on the 
southeast side, and at the surface the 
basal clays of the Indio formation are 
brought up into contact with a medial 
sandy member. The fault is well 
exposed where it crosses the San 
Marcos River about 6 miles northwest 
of Luling. 
In this field the Eagle Ford shale is 
35 feet thick; the Buda limestone, 40 
feet; and the Georgetown, a com 
limestone, 50 feet. The normal dip of 
the strata in this region is only 1°-2° 
that the Edwards limestone, of which 
the upper part is porous, is about 730 
feet thick. It is underlain by 1,450 
feet of Glen Rose limestones and clays 
(Brucks) and Trinity sands, the Trinity 
lying on pre-Cambrian 
depth of about 4,790 feet. 
p. 65.) Into this schist 
continued nearly to 8,000 feet without 
the slightest prospect of reaching its 
base or of finding petroleum, 
