A SHORT NOTE ON THH OÍL FIELDS OF MÉXICO L25 



tunately, data collected during drilling and observations 

 of the experts in this and other particular cases never come 

 to the public domain. 



I have seen many cases of very small exudes dropping 

 slowiy from narro w cracks and little faults in the cliffy 

 banks of rivers where the shales are cut by erosión. This is 

 the case inseveral places on the rivers Tecolutla, Tuxpan, 

 Calabozo, Panuco, Tamesí, Valles, etc., etc. 



The unimportant veins of albertite and grahamite, so 

 well known in the coast, proceed probably from oíd exudes 

 filling cracks and fissures where the "chapopote" dry slowiy, 

 becomes a little oxydized and then subjected to pressure. 



Lighter oil than that commonly found on the coast (Cen- 

 tral oil lands) appears to be found at shallower depths in 

 the disturbed shales near the limestones at the foot hills 

 of the Eastern Sierra Madre mountains. This seems to 

 coincide, as in Aquismón, with local impregnation of the 

 limestones by light oil producís. In this case the oil prob- 

 ably comes up through the contact between the shale and 

 the limestone which lie in unconformity. 



While in this upper belt of the oil country conditions are 

 still entirely unknown, it seems to the writer that .a pos- 

 sible source of petroleum exists in this long belt, under 

 conditions probably different from the áreas already known 

 or in the way of development nearer the Mexican Gulf 

 seashore or in the estuaries bordering it. 



I have carefully studied under the microscope the sandy 

 sediment accompanying the oils coming from several wells; 

 especially from those near Tampico. This sediment is com- 

 posed of minute shale splinters and roundcd grains of bas- 

 altic material, similar to the rock of the necks. The volcanic 

 origin of certain mounds and the influence of volcanic action 

 as facilitating the accumulation of oil is demonstrated by 



what we have seen of volcanic rock particles brought with 



