Relations of the oils to structure 645 



The other external lateral factors of limitation, including faults, veins, 

 and dikes, with their associated selvages, shear zones, etcetera, are prob- 

 ably of little importance in the Appalachian field, although both faults 

 and dikes are known. 



DIPS 



In general, oil is found in the Appalachian field only where the dips 

 are under 3 degrees, although an occasional pool is found where the pre- 

 vailing dips are from 3 to 10 degrees, as at Gaines, Pennsylvania. John- 

 son & Huntley^^ found that in a district examined by them in south- 

 eastern Ohio and northern AYest A-'irginia the largest number of pools 

 occurred where the average dip was 20 feet or less per mile. About three- 

 fourths as many were found 'wliere the dips were 40 feet, and a third as 

 many where they were 60 feet per mile. About 85 per cent of the pools 

 were in rocks dipping 1 degree or less. 



Somewhat similar relations obtain throughout the entire Appalachian 

 oil field, although the percentage of pools in the beds of the very lowest 

 dip are probably somewhat lower, taJving the district as a whole, than in 

 the district mentioned. 



Production 



DEVELOPED AREA 



The coal basin, or synclinorium, between the Appalachian Mountains 

 and the Cincinnati anticline is about 800 miles long, and ranges down- 

 ward in width from 300 miles at the New York line to 150 miles in Ken- 

 tucky, 50 miles in Tennessee, and 25 miles in Alabama. The total area 

 is about 70,000 square miles. 



While the greater part of this area is oil- or gas-bearing to some extent, 

 most of the production comes from a strip about 25 miles broad, lying 

 parallel to and just outside the westernmost strong fold of the Appa- 

 lachians from the N'ew York line to central West Virginia, a distance of 

 300 miles. The area is 7,500 square miles, or a little over 10 per cent of 

 the area of the basin. 



The area of the xVppalachian oil field has been estimated at 2,504 square 

 miles, which would be equivalent to about 3.6 per cent of the basin and 

 33 per cent of the oil belt. 



The developed area by States is as follows :^^ 



18 Ibid., p. 80. 



10 David T. Day : "Map of Known Producing Oil and Gas Fields of the T^nited States 

 in 1908." Min. lies. U. S., 1908, pt. 2, pi. 1, 



