OIL AND GAS LANDS. 117 



from Carboniferous strata. In the Mid-Continent field, which em- 

 braces Missouri, Kansas, and Oklahoma, the petroleum has accumu- 

 lated in rocks of the Pennsylvanian and Permian series. In the Gulf 

 field, which includes the Coastal Plain of Louisiana and Texas, the 

 petroleum-yielding rocks are Mesozoic and Cenozoic in age, being 

 assigned in part to Cretaceous and in part to Tertiary formations. 



In the Rocky Mountain fields the productive formations range in 

 age from late Paleozoic to late Mesozoic. The Wyoming fields pre- 

 sent perhaps the greatest range of occurrence, yielding oil from strata 

 belonging to the Carboniferous, Triassic, Jurassic, and Cretaceous 

 systems. The Colorado and New Mexico fields thus far developed 

 obtain their oil from strata included entirely within the Cretaceous, 

 and the small quantity of oil produced in Utah is derived from rocks 

 assigned to the Carboniferous system, although indications of oil are 

 found at certain localities in the Jurassic and Cretaceous rocks. 



In the Pacific coast region the important accumulations of oil are 

 found chiefly in Cenozoic rocks, although in certain fields an out- 

 put of local importance is obtained from late Mesozoic rocks. In 

 Ventura County, Cal., the principal oil-yielding formations are 

 classed as Tertiary and range in age from Miocene to Pliocene. 

 Along the west side of the San Joaquin Valley the range is greater, 

 the oil extending downward into the upper members of the Cretaceous 

 system. In the Kern River field, on the east side of the San Joaquin 

 Valley in Kern County, oil is obtained from rocks of late Miocene or 

 Pliocene age. In Santa Barbara County the oil is derived chiefly 

 from early Miocene rocks. In portions of Oregon and Washington 

 small amounts of oil and gas have been obtained from rocks assigned 

 to the Eocene and Miocene series. 



Despite this wide distribution of fluid hydrocarbons the conclusion 

 does not necessarily follow that accumulations of asphaltum, oil, or 

 natural gas may be found in any area of sedimentary rocks, for such 

 accumulations take place only where all the essential conditions gov- 

 erning origin, adequate storage facilities, and favorable structure are 

 fulfilled. 



CLASSIFICATION OF OIL AND GAS LANDS. 



The immediate purpose of the classification of oil and gas land 

 is to withhold from entry all lands containing valuable deposits of 

 fluid hydrocarbons pending the enactment of adequate legislation 

 providing for their disposition. The ultimate purpose of the classi- 

 fication is to determine the position and extent of the areas whose 

 value for their deposits of oil or gas, whether proved by actual 

 drilling or indicated by favorable geologic conditions, is greater than 

 their value for agriculture or other purposes and to provide for a 

 disposition of the deposits in accordance with this greater value. 



