STATE GEOLOGIST. 319 
ereat volume of oil that has been taken from it in places,, as for illustra- 
tion the Scio field. This appears all the moré remarkable when it is re- 
called that the so-called pay-streak usually composes a small part only of 
the rock. Sands of this character do not yield great wells, but their life 
as a rule is long. These characters are certainly in harmony with the 
porosity of the rocks. The Berea is the finest grained of the important 
oil or gas sands of the state. 
Sandstones grade imperceptibly into conglomerates, and hence it is 
not easy to say when one leaves off and the other begins. Many of the so- 
called conglomerates of Ohio vary in texture rapidly, changing in a short 
distance to a sandstone. The Big Injun, Keener, Macksburg 500-foot, and 
First Cow Run sands are conglomeritic in places, but more commonly 
they are coarse sandstones. They make excellent reservoir rocks, and the 
wells sometimes have large initial productions. The decline, however, is 
almost invariably more rapid than in the Berea. The production is often 
long maintained, as is illustrated by wells at Joy, Cow Run and other 
places. 
Shales are not important sources of either oil or gas though small 
quantities of both are often found in them. In the coarser grades of these 
rocks oil and gas may occupy the spaces between grains, but in the finer 
erades the fuels in question probably lie between the layers of the rock 
rather than between the component particles. | 
The necessity of an impervious cover is apparent. Without it the gas 
would have risen to the surface and been lost ages ago, and the more 
volatile parts at least of the oil would have met a similar fate. Not un- 
commonly the rock is very compact at the top forming the “cap” of the 
driller. This may serve to retain the oil and gas below. Generally, how- 
ever, a bed of shales lies above the formation, and serves to prevent the 
ascent of the fluids. A thin bed of fine clay also would serve admirably 
to seal in the oil and gas. 
The third geological condition is structural, and is commonly known 
as the anticline or terrace. This permits the oil and gas of a relatively 
large area to accumulate in a much smaller one. This theory has been 
strongly urged by White and Orton, and in a more general way by others 
at an earlier date. It is very generally accepted by geologists and almost 
equally so by laymen. In many cases important reservoirs have been 
located by applying the principle. Thus in eastern Ohio Orton predicted 
the presence of oil in the Moore’s Junction field west of Marietta, and cor- 
rectly located the Snyder and Bricker pools in Harrison county. White 
has been still more successful in West Virginia and Pennsylvania. Among 
other pools in eastern Ohio that have been demonstrated to lie on anti- 
clinals may be mentioned Macksburg, Cow Run, Newell’s Run and Sisters- 
ville. In the northwestern part of our state the rocks form a broad arch, 
dipping to the northwest on one side and to the southeast on the other. 
