EFFECT OF IGNEOUS INTRUSIONS ON OIL 671 
the Cretaceous-Eocene shales certainly afford one of the most 
effective means to concentrate whatever hydrocarbons might have 
been disseminated throughout these beds. 
--FOCENEA DAZLA 
\ 
N 
SSR ees 
LMMESTONES 
N7A DAVAL FS 
Mi 
| 
| 
E 
< 
a. 
3 < 
Sale <a: Soret 
S < < SN 
< Ss < 
<8 
Sr =e 
Ce 
ee 
< 
< 
< 
HI 
! 
( 
iS 
4 
S 
\ 
Fic. 3.—Hypothetical section of basalt intrusion penetrating the series of 
Cretaceous limestones and shales without disturbing the Cretaceous-Eocene shales, 
and giving rise to a dome of fractured and porous material, effectively covered with 
an impervious cap-rock. The large production of some of the Mexican gushers can 
readily be accounted for on this hypothesis. 
Finally, it is apparent that if the Cretaceous limestones yielded 
the oil, it must have been before the event which changed them to 
their present compact and rather crystalline nature, and it is 
probable that such a condensation of the oil was coincident with 
