HAYES AND 
KENNEDY. 
SPINDLETOP POOL. 7l 
active. From the samples of the oil rock thus far obtained it is 
impossible to make any accurate determination of the relative volume 
of the open cavities, but the proportion can hardly be less than one- 
third, and may be somewhat more when account is taken also of the 
minute spaces between the crystal grains of the more compact porl ions 
of the rock. 
The exceptional character of this oil rock explains in a measure the 
remarkable features of the Spindletop pool. Its extreme porosit} 7 
favors the storage of a very large volume of oil, and also favors the 
yielding of this oil with great rapidity when the reservoir is tapped. 
It also favors the early exhaustion of the oil in the pool and its rapid 
replacement by the underlying brine. 
From some of the wells, along with the dolomite large pieces of 
crystalline gypsum or selenite have been thrown out by the escaping 
oil. Their surfaces are always deeply corroded, giving evidence that 
they have been subjected to the action of some solvent. 
Another important accessory mineral in the oil rock is native sul- 
phur. Large crystals, an inch or more in length, have been obtained 
from many of the wells, and it is reported by several of the drillers 
that the oil rock is overlain by a heavy bed of sulphur. In the 
National Oil and Pipe Line well No. 1 this sulphur deposit is claimed 
to have a thickness of 40 feet. A large amount of material was 
brought out by the bailer, consisting of coarse sand, about 25 per 
cent of which was pure sulphur and the remainder granular dolomite 
and crystalline calcite. The grains are slightly rounded, probably 
by the friction of the bailer, and the sand is doubtless derived from 
the disintegration of a soft dolomite in which the sulphur ciystals are 
embedded. In wells Nos. 2 and 3 of the same company a similar bed 
of pure sulphur is reported, separated from the oil rock by from 23 to 
2G feet of sulphur-bearing sand. In the Heywood wells Nos. 1 and 2 
this bed of sulphur is also recorded, and there is said to be about 70 
feet of it in Gladys well No. 3. A similar bed of sulphur is claimed 
to underlie 10 feet of oil sand in the Higgins well No. 1, but does not 
appear in Higgins well No. 2 nor in the Lucas well. It is also absent 
in the Geyser Oil and Development well on the north side of the hill. 
BEDS UNDERLYING THE OIL ROCK. 
While the actual thickness of the oil-bearing beds throughout the 
greater part of the pool is undetermined, certain minimum thick- 
nesses are known, as wells have been drilled as deep as 77 feet into 
these beds, and one well has gone down to a depth of 96 feet without 
passing through the oil rock. 
Only a few wells on Spindletop have passed entirely through the 
oil rock, and there is therefore little information available concerning 
the character of the underlying rocks. The Robertson well, toward 
the western side of the pool, is reported to have passed through 50 
