274 I. C. WHITE PETROLEUM FIELDS OF NORTHEASTERN MEXICO 



Two of these are of special interest, namely, Cerro Viejo and Moralillo. 

 At the former a well was sunk 25 to 30 years ago and large quantities of. 

 oil were found, since the easing is still in the well, and when the gate 

 valve is opened (he oil, a heavy black fluid, pours out in a steady stream. 

 The locality, however, is in the midst of a tropic jungle remote from 

 any means of transportation, and its former owner (reported to have 

 been a. resident of Massachusetts) does not appear to have realized that 

 the oil had any value, although the tract on which this well was drilled 

 extends along the western hank of the Buena Vista Kiver, only 100 feet 

 distant from the great Potrero del Llano well. 



The seepages at Moralillo are interesting, since at one of them the oil 

 i oozing from the joints of the basalt, proving not that the oil had an 

 igneous origin, as Presidenl Fairehild and Mr. Eugene Ooste would prob- 

 ably insist, but that the path of least resistance to the surface from its 

 oiioin in the sedimentary beds below was in this case not through the 

 close-grained shales immediately above, but along the fracture made by 

 the basalt,' and out to the surface through the more or less open joints of 

 (Jie same. Thai the conditions Tor accumulation of oil and gas in com- 

 mercial quantity are (\uv primarily to the upward bulging of the strata 

 produced by the out (low of the basalt through the sodimentaries, whether 

 in the shape of cones and dikes which reach the surface, or laccolites 

 below the same, all agree who have studied the matter. Of the several 

 ideas already published on the subject and illustrated, the first was by 

 Frederick G. Clapp, Fellow of this Society, in Economic Geology, Volume 

 VI I, No. 4, for June, 1912, pages 364 to 381, inclusive. 



The other illustrations represent the ideas of V. R. Garfias, of Los 

 Angeles, who, from the experiment of driving a nail through an unbound 

 book with thicknesses comparable to that of the intrusions of basalt and 

 the adjoining sedimentaries, secured rents and distortions in the leaves 

 of the paper similar to that shown in these diagrams, as illustrated in 

 his article on this subject published in the Journal of Geology for Octo- 

 ber-November, L912, Volume XX, No. 7, pages 666 to 672, inclusive. It 

 is quite probable that the views of both Clapp and Garfias are correct 

 and that all these types of disturbance may exist in the regions where 1 

 the seepages oecur. The groat well. Casiano Xo. 7, is drilled so close 

 to the hill of diabase, which crops within 100 to 500 feet of the well, 

 that if the plug of basalt were conical the boring would undoubtedly 

 have penetrated the same before it leached a depth of 2,112 feet, where 

 the oil was found in the top of the Tamasopa limestone. 



Chijol well \o. 5 of the Ebano group, where a dike of basalt 'U \\>vi 

 thick was struck at L16 feet, would also appear to favor the occurrence 

 of structures like those suggested by Garfias. 



