628 M. L. PULLER APPALACHIAN OIL FIELD 



very suggestive. The history of oil fields in the United States may be 

 divided into three periods : 

 I. Period of unconscious application of certain geological factors 



(1859-1888). 

 II. Period of application of anticlinal principle (1888-1900). 

 III. Period of intensive application of geology (1900 to date). 



In the first period, in spite of the unconscious application of geological 

 strike through "degree lines/' there was, as elsewhere explained, no real 

 understanding of either stratigraphy or structure, and production in- 

 creased very slowly. By 1888 it had already dropped off several million 

 barrels per annum. 



Several years before this date Doctor White began the application of 

 the anticlinal principle to the location of pools in Pennsylvania and West 

 Virginia, but the influence was most apparent from 1888 to 1892, when 

 the production jumped from sixteen to thirty-six million barrels a year. 

 From this maximum it has slowly declined. 



The period of intensive application of geology began about 1900, with 

 the greater utilization of the reports of the National Geological Survey, 

 and was soon followed by the employment of geological experts and large 

 corps of corporation geologists. In the Western fields the effect was very 

 marked, as shown by figure 1 ; but the results were less apparent in the 

 East, for the reason that the field was in its decline and the operators 

 were very conservative. Geology, nevertheless, has probably had a mate- 

 rial effect in sustaining production and giving it a much slower decline 

 than it would otherwise have had. 



Stratigraphy 

 formations represented 



Although most of the geological column from Cambrian to Carbonif- 

 erous is represented in the strongly folded regions of the Appalachian 

 Mountains and underlies the oil field proper, at least in its northern por- 

 tion, much of it is beyond the present limits of the drill. 



In northwestern Pennsylvania tliere is little Carboniferous except on 

 the hilltops, but at the southwest corner of the State there is nearly 3,500 

 feet exposed at the surface or encountered in wells. The Devonian shales 

 form much of the surface in northwestern Pennsylvania and are found 

 in the wells in the southwest counties, in which they have been penetrated 

 to a depth of not less than 4,000 feet. The 7,100-foot McDonald well, in 

 this section, ended in the Salina formation, whicli would give to the De- 

 vonian a total thickness of more than 5,000 feet. 



