254 I. C. WHITE PETROLEUM FIELDS OP NORTHEASTERN MEXICO 



general manager of the Mexican Petroleum Company's interests in the 

 Republic and one of the ablest business men in the petroleum world. 



Geology of the Mexican Petroleum Fields 



It has long been recognized, both by geologists and practical petroleum 

 operators who lay no claims to geological knowledge, that disturbance of 

 the sedimentary beds, so as to tilt them out of the horizontal position to 

 a greater or lesser extent, is an essential factor in the accumulation of 

 oil and gas into pools or deposits of commercial value. In the Appa- 

 lachian fields of Pennsylvania, West Virginia, Ohio, Kentucky, etcetera, 

 these disturbances partake of the character of anticlinal and synclinal 

 waves of small amplitude practically parallel to and made by the same 

 orogenic movements which created the vast arches and folds in the rocks 

 of the Alleghany Mountain region. The same structural features hold 

 true for the oil regions of Indiana, Illinois, Oklahoma, Colorado, Wy- 

 oming, California, etcetera, and also hold true for the other great oil 

 fields of the world, as in Russia, Rumania, and India. Along the Gulf 

 coast of Texas, however, as illustrated at Beaumont, other factors of sedi- 

 mentary disturbance than mountain-made folds in the earth's sedimentary 

 crust come into play, and we get a series of domes where the rocks dip 

 away from the highest point in every direction, or in a quaquaversal 

 manner, instead of the anticlinal, synclinal, or monoclinal features of 

 geologic structure so common in the Appalachian oil and gas fields. 

 The formation of these dome structures in the rocks of Texas and Lou- 

 isiana is explained in a plausible way by Prof. Gilbert D. Harris, former 

 State Geologist of Louisiana, as due to the immense lifting force gen- 

 erated in the crystallization of salt in the vast beds of this mineral which 

 underlie the coastal plains region of the States in question. 



In passing southwestward from Texas into the Republic of Mexico a 

 third agency of geologic disturbance of the sedimentary beds becomes 

 operative, namely, the uplifting effects of volcanic dikes, necks, laccolites, 

 and other forms of igneous activity in tilting the sedimentary beds into 

 domelike structures, fracturing and faulting even the close-grained 

 shales and sending tongues of porous lava into them in such a manner 

 as to make large reservoir spaces where none previously existed, and per- 

 mitting the petroleum and its accompanying natural gas to leak upwards 

 to the surface as seepages very often in immediate contact with the 

 basaltic lava, and sometimes through joints of the lava itself, as at 

 Moral illo. These intrusions of volcanic materials have accomplished in 

 the Mexican Gulf coast fields what orogenic movements and crystalline 



