PETROLEUM AND NATURAL GAS. 65 
Beailsville and Zollarsville, a few wells occurring nearly to the cen- 
ter of the basin. The apparent disregard of structure here may per- 
haps be due to the nonparallelism of the oil sands and the Pittsburg 
coal, but the data at hand are not sufficient to permit the accurate 
drawing of contours on any sand. Near the axis of the syncline, 
southwest of Beailsville, oil has been struck in several wells. 
Summary. — The distribution of oil and gas in the quadrangle as a 
whole can be said to show a fair agreement with the geologic struc- 
ture. The most favorable location for oil seems to be on the flanks of- 
the anticlines, and for gas either on the broad anticlinal arches or the 
upper part of the synclinal slopes — always, however, higher up the 
slope than where oil is found. 
ORIGIN OF OIL AND GAS. 
The theories for the origin of petroleum and natural gas can be di- 
vided into two groups, viz, (1) those which refer these products to in- 
organic action or chemical affinity in mineral matter, and (2) those 
which regard them as due to partial decomposition of vegetable and 
animal matter stored in the rocks. The various modifications of these 
theories have been discussed in considerable detail by Edward Orton. a 
The theory now most generally accepted by geologists is briefly as 
follows : 
When the Paleozoic rocks were deposited they contained large 
amounts of carbonaceous matter, the remains of animal and vegetable 
organisms. This material was present in sufficient quantities to give 
ris.e to oil and gas, through the process of decomposition and the phys- 
ical and chemical changes to which it has been subjected during geo- 
logic time. The products may originally have been formed in greater 
abundance in shales, but when once formed they probably migrated 
into the more porous rocks, especially sandstones, in which they are 
now held. As there are at present no surface indications of the pres- 
ence of either oil or gas, it is probable that considerable quantities have 
escaped from outcropping strata during the process of erosion. 
MISCELLANEOUS NOTES ON OIL AND GAS. 
CHARACTER OF THE OIL. 
Washington County lies in what is known technically as the south- 
west district of Pennsylvania and northern West Virginia. All the 
oil produced in this district is a high grade of petroleum. It has a 
paraffin base and a high degree of purity. In color it varies somewhat. 
Though generally green, it is sometimes black, and in a few cases 
amber or even nearly transparent. 
a Report Geol. Survey Ohio, vol. 6, Economic geology, 188S, pp. 60-83. 
Bull. 300—07 5 
