THE EFFECT OF IGNEOUS INTRUSIONS ON THE 
ACCUMULATION OF OIL IN NORTH- 
EASTERN MEXICO 
V. R. GARFIAS 
Los Angeles, Cal. 
The region where the occurrences herein noted were observed 
comprises the portion of the Mexican coastal plain between the 
Panuco and Tuxpan rivers in the northern part of the state of 
Vera Cruz. 
The formations involved in the geology of this area are of 
Cretaceous and Tertiary age, with unimportant Quaternary 
deposits near the coast. For convenience, they will be separated 
according to lithology into three divisions; the lower of which is 
made up of several thousand feet of limestones overlain by a 
series of alternating limestones and shales, the whole of Cretaceous 
age; the middle, of uniform shales and marls with a total thickness 
of about 3,000 feet, of upper Cretaceous-Eocene age; and the upper, 
of Tertiary sands, clays, limestones, and conglomerates, having an 
aggregate thickness of about 700 feet. 
The marked characteristic of the geology of this region is the 
large number and magnitude of the volcanic intrusions, the rem- 
nants of which are represented in places by isolated basaltic cones, 
breaking the monotony of the coastal plain. The volcanic activity 
is more pronounced in the southern portion of the area, attaining 
its greatest development in the Otontepec range, an irregular 
basaltic mass about 2,000 feet high. The location of many of the 
intrusions was probably controlled by well-defined fault lines, and 
cross-faulting or any decided weakness of the underlying basement 
may also have played an important part in their distribution. 
The intrusions occurred during late Tertiary or possibly early 
Quaternary times, and consist of basalt accompanied in places by 
volcanic ash and conglomerate. Most of the surface indications 
of oil are closely associated with the basalts and hundreds of such 
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