256 I. C. WHITE PETROLEUM FIELDS RTHEASTERN MEX 



Above the Mendez beds come Tertiary sandstones and shales several 

 hundred feet thick, along with Quaternary unconsolidated deposits, all 

 dipping toward the Gulf coast, together with the underlying Mendez. San 

 Felipe, and Tamasopa beds, so that here in Mexico we appear to have in 

 ideal form the three conditions under which petroleum and natural gae 

 can accumulate into pools of commercial value, namely : 



Sedimentary beds tilted into domes, anticlinal s. monoclinals. and 

 other forms of relief. 



Very porous rocks and large reservoirs, either in the Tamasopa 

 limestone, with much crystalline and solution cavities, as indicated by 

 limestone thrown up by the oil and gas flows, and also 

 much reservoir space in the Mendez and San Felipe beds through intru- 

 sion of dikes and sills of perhaps vesicular basalt breaking and fracturing 

 -edimentaries and adding to the reservoir space in the shales through 

 pulsating movements of these intruded igneous masses during periods of 

 active eruptions, as believed by Orclonez. 



An impermeable ^an Felipe and Mendez beds, with much 



marl, and close-grained shales, and only permitting the oil an-' a 

 ,~ 'he surface in small quantities along narrow fissures, fan 



and crevices, whe stored by the upthrust of basaltic dikes and 



bathe. 



That the Tamasopa. or "basalt limestone of the drillers, is the 

 source >f the petroleum in these Mexican fields appears to be amply 

 demonstrated by the fact that all the large gushers. 1: 



iano and the famous Potrero del Llano well, obtain their oil in the 

 top of this great limestone formation. 



3 OF THE 



The character of the beds overlying the Tamasopa limestone is shown 

 he following records of Casiano wells nd T and some from 



near Ebano : 



Ju< U Yo. 6 



rted drilling April 7. IS 

 Feet In. 



Yellow clay. 



y shale. 

 60 I unscrewed. 



76 7 Landed 16-inch casing. 

 Pnr in 12^4 -inch casing. 



hole: filled hole up to 95 feet April _ 

 1 hole: filled hole op to 235 feet: hole *rraiirhteued up May 12. 



