558 F. G. CLAPP CLASSIFICATION OF PETROLEUM AND GAS FIELDS 



Geological Society of Washing-ton on March 9, 1910/^ and puhlished in 

 September of that year/*^ While adequate to include most producing oil 

 and gas structures known at tlie time, it manifestly needed further ex- 

 planation and subdivision: so that on December 29, 1910, a paper on 

 certain aspects of monoclinal accumulation was presented before the (tco- 

 logical Society of America in Pittsburgh, Pennsylvania, and published in 

 January, 1911,^^ previous to which time monoclinal pools had been sup- 

 posed to exist chiefly in terraces. This paper was followed in June, 1912, 

 by one on quaquaversal or dome structures.^^ A few facts were added in 

 1913i» and a few additional facts in 1916.^" 



In 1915 a classification of seepages or oil springs was proposed by De 

 Golyer^^ as follows : 



I. Seepages associated with igneous intrusions. 



(a) At contact zones of volcanic plugs and sedimentary rocks. 

 (&) At contact zones of dikes and sedimentary rocks. 



(c) Through cracks and fissures in the igneous rock itself. 



(d) As intrusions in the igneous rock. 



(e) From metamorphosed rock above an intrusion which does not out- 



crop. 



II. Seepages not associated with intrusions. 

 (a) At crest of domes or anticlines. 

 (&) Along marked fault or fissure planes. 



(c) From steeply dipping strata. 



(d) Isolated occurrences of uncertain relations. 



The classification of seepages did not modify the classification of struc- 

 tures, but furnished several ideas for its further subdivision, and is men- 

 tioned here on account of its general bearing on the subject. Since little 

 criticism has been made of the structural classification as proposed by 

 the present writer, which appears to have been quite generally accepted, 

 it now seems time to bring it into final form, which is done herewith. 

 The subdivision has been carried still further and several new classes 

 added, in accordance with suggestions received from time to time. 



IS Science, n. s., vol. 31, no. 801, May 6, 1910, pp. 718-719. 



i« A proposed classification of petroleum and natural gas fields based on structure. 

 Econ. Geol., vol. v, no. 6, pp. 503-521. 



" Notes on the occurrence of oil and gas accumulation in formations having mono- 

 clinal dips. Econ. Geol., vol, vi, no. i, 1911, pp. 1-12. 



18 The occurrence of oil and gas deposits associated with quaquaversal structure. 

 Econ. Geol., vol. vii, no. 4, 1912, pp. 364-381. 



" Outline of the geology of natural gas in the United States. Econ. Geol., vol. viii, 

 no. 6, 1913, pp. 517-542. 



20 In a special chapter by F. G. Clapp : Bacon and Hamor's "Principles of oil and gas 

 production," vol, 1, 1916, pp. 34-68. 



a E. De Golyer : Econ. Geol., vol. 10, 1915, p. 654. 



