viii, a, 5 Pratt and Smith: Petroleum Resources 343 



to the northern limb of the Malipa anticline. These are found 

 along Vigo River, and dip about 45° to the north-northeast. 

 Farther north the dips and strikes are much confused, and the 

 structure is not clear. The volcanic agglomerate is encountered 

 at the head of Tangob Creek. In this vicinity the Vigo shale dips 

 steeply to the east-northeast in perhaps a majority of the ex- 

 posures, but its relations are not uniform. 



Bato anticline. — Near the small village of Bato, north of 

 Cabongahan, the lay of the beds indicates a local anticline in the 

 Vigo shale, the axis of which is roughly parallel to the Central 

 anticline. Like the Malipa anticline this fold appears to be a 

 minor overturn in the general eastern limb of the Central anti- 

 cline. It is a sharp flexure, the strata in each limb dipping at 

 angles of 60° or more, but is persistent over a length of a few 

 hundred meters only. The stream between Bato and the ridge 

 to the east appears to follow the axis of this anticline. The Bacau 

 stage of the Vigo shale is exposed along its crest and dips away 

 from the stream line on either side. The upper formations 

 appear on top of the Vigo shale in the eastern limb, forming 

 the high ridge between the anticline and the eastern coast. The 

 dip in the uppermost beds is from 30° to 45° east-northeast. 

 Pusgo Bay which lies off the eastern coast at this point occupies 

 a syncline, and San Narciso Peninsula, east of the bay, is a mon- 

 ocline dipping gently westward toward this syncline. West of 

 the axis of the Bato anticline only Vigo shale is exposed and 

 the westerly dip of its beds persists for a short distance only, 

 beyond which the shale dips steeply to the east-northeast, mark- 

 ing the eastern limb of the Central anticline. 



In the Florence, Colorado, oil field, 16 the stream lines are some- 

 times marked by small sharp anticlines, which are attributed to 

 purely superficial phenomena, such as the expansion of rocks 

 through weathering and consequent thrust of surface beds into 

 the valleys formed by streams. It is possible that the Bato 

 anticline is of this type, but the fact that petroleum is found 

 along its crest argues that it is more than superficial in effect, 

 since petroleum is found usually in true anticlinal zones, else- 

 where in the field. 



Ayoni anticline. — Inland from the villages of Ayoni and Bon- 

 doc on the west coast, the dip measurements and the hill forms 

 reveal an upward flexing of the strata along a line directed 

 north 35° west. This axis is about 1,200 meters and 2,000 

 meters from the coast at Ayoni and Bondoc, respectively. The 



"Washburne, C. W., Bull. U. S. Geol. Surv. (1909), 381, 49. 



