120 CLASSIFICATION OF THE PUBLIC LANDS. 



the folds the ultimate place of accumulation. Experience has shown 

 that only under exceptional conditions may considerable accumula- 

 tions of light paraffin-base oils be expected in monoclines, although 

 in many places the monoclinal structure lends itself to the accumu- 

 lation of heavy asphaltum-base oils. 



The presence or absence of water in the formations of an oil-bear- 

 ing region is a factor in the classification only as it affects the accu- 

 mulation of the hydrocarbons, determining very largely their relation 

 to the structure, as already explained. Whether or not it is present 

 in the petroliferous strata must be known before a satisfactory classi- 

 fication can be made. 



The maximum depth at which accumulations of oil or gas will 

 warrant the classification of an area, as oil land is a matter that de- 

 mands careful consideration for each field. The factors that deter- 

 mine this depth limit are primarily the richness and the continuity 

 of the oil-bearing zones, secondary consideration being given to the 

 quality of the oil, present market conditions, and transportation 

 facilities. Thus in certain areas where production is large and the 

 oil-yielding zones are believed to continue productive to considerable 

 depth, lands beneath which the productive zone lies at a computed 

 depth of 5,500 feet have been classified as oil lands. On the other 

 hand, in areas where the geologic conditions preclude a large accumu- 

 lation of oil and indicate a doubtful continuity of the oil-bearing 

 zones, depth limits as low as 3,000 feet have been fixed. That quality, 

 market, and transportation facilities should receive only incidental 

 consideration becomes evident when it is realized that deposits of 

 low-grade oils that can not now be commercially exploited may, in the 

 not distant future, as a result of improvements in methods of drilling 

 and refining, become important contributors to the Nation's fuel 

 supply ; that the use of oil is practically just beginning, and it ap- 

 pears certain to build for itself a market far greater than it at 

 present commands; and that with the advance of settlement or the 

 beginning of production transportation facilities will be provided for 

 fields now remote and essentially undeveloped. To many persons a 

 maximum depth limit of 5,500 feet appears excessive, but to one 

 who has acquainted himself with the rapid progress in well-drilling 

 methods and machinery during the last decade this limit is 'far from 

 imreasonable. In many of the California fields wells drilled to 

 depths of 3,500 or 4,000 feet are by no means uncommon, and in for- 

 eign countries and at a few localities in the United States wells 

 more than 5,000 feet deep have been drilled. In the Kern River oil 

 field, California, one well has a depth of 5,135 feet ; in the Midway 

 field of the same State a well whose depth is slightly more than 

 5,000 feet is reported ; and in the vicinity of Los Angeles a well was 



