griswold] STRUCTURAL WORK IN EASTERN OHIO OIL FIELDS. 337 
to the oil-bearing strata, so that each oil operator might himself study 
the structural conditions which have produced valuable oil pools in 
the past. The many failures of those hunting for oil on the anti- 
clinal theory have thrown discredit upon the ability of geologists to 
assist in the location of productive territory. Most of these failures 
have been due to lack of knowledge concerning the geologic structure 
or to the absence of other conditions necessary for the accumulation 
of oil. Although geologic structure is of primary importance, it is 
only one of three or more conditions that must be fulfilled in order to 
produce an oil pool of economic value. 
Porosity of the sand. — The condition of the sand as to degree of 
porosity and capability of holding a fluid is a factor of great impor- 
tance, and One that, with the geologic structure, governs the accu- 
mulation of oil. It is evident that when a sand is loose and composed 
of large grains fluids may pass easily between the particles, and that 
a much less slope or grade would cause salt water, oil, and gas to 
accumulate in separate bodies than if the sand were fine and close 
grained. The condition of the sand can in no way be determined 
except by the sinking of a test well. , In many instances, within a dis- 
tance of 600 feet from wells of large production from a good sand, 
other test wells have found the sand hard and closely cemented and 
incapable of holding fluids of any description. 
Degree of saturation of sand and position of water line. — The sat- 
urated condition of the porous stratum is another factor of primary 
importance in the formation of a pool of oil, and one that has not been 
given due prominence. The water-line theory, as advanced by the 
writer, assumes that the tops of the anticlines often contain no liquid 
upon which the oil may climb, so that, while the gas from its lesser 
gravity may pass on to the very highest point of the stratum in which 
it is contained, the oil will rise only so far as it has the water for a 
supporting medium. Tfre height of the water line thus gives a line of 
equal elevation along the strike of a stratum, which, when once deter- 
mined by the drill, should be followed to keep on the line of oil-pro- 
ducing territory. The belt of oil accumulation may be illustrated by 
a comparison of it to the sand beach along the shore of the ocean, 
where the sea represents the salt-water area, the upland the area of 
dry rock, and the sand the belt of saturated oil stratum. This belt, 
like the ocean beach, may be narrow or widen out over considerable 
space, so that the saturated portion of the oil stratum may be wider or 
narrower, forming what appears to be a line of separate pools. The 
amount of saturation is different in different sands and also in A T arious 
parts of the same sand. In a sand containing only small saturated 
areas the oil accumulation may be low down in the syncline, with an 
area reaching far above it that upon test would only produce dusters. 
Each independent structural basin must be considered separately as 
to the location of the water line. Great assistance would have been 
Bull. 2113—03 22 
