226 GEOLOGICAL RECONNAISSANCE OF THE DOMINICAN REPUBLIC. 



but no trace of petroliferous material was found. The mud in the stream 

 bed had an odor of hydrogen sulphide. At the time of the visit much rain 

 had recently fallen, and with the rise of the creek the indications may have 

 been obscured. The rocks in this vicinity are all early Tertiary or older 

 and are so greatly sheared, twisted, and faulted that oil could hardly be 

 trapped in them except in small quantities. The discovery of any petro- 

 liferous material here, however, would indicate that the "older series" 

 may possibly contain oil elsewhere at places where the beds are not so 

 greatly folded and faulted. 



Practically all the rocks that form the hills from Ocoa Bay eastward to 

 Rio Nizao are of Oligocene age or older (Eocene at station 8614, 5.2 kilom- 

 eters east of Bani), the principal exception being the Pliocene or more recent 

 conglomerates that lie nearly flat and form terraces that reach altitudes of 

 a few hundred meters. The early Tertiary or Cretaceous strata consist of 

 gray to dark limestone, purplish to reddish slaty shales or shaly limestone, 

 sandstone, and calcareous sandy shale, all of which are greatly distorted 

 and broken by faulting. Rio Ocoa, in its course from San Jose" de Ocoa to 

 Arenoso, follows one of these faults, the uplifted side of which is preserved 

 in El Numero, a southward-trending ridge west of Rio Ocoa. 



SUMMARY OF ECONOMIC GEOLOGY. 



Oil and gas. — The locality at Higuerito, near Azua, has been the principal 

 center of interest as a possible commercial oil field and is the only place 

 where wells have been drilled for oil. The results have not been very 

 encouraging, but drilling has been resumed in the belief that some of the 

 earlier wells might have been valuable but were lost through the encroach- 

 ment of salt water, due to mismanagement. 



There are large areas in the provinces of Barahona and Azua that are of 

 sufficient interest as possible oil fields to warrant detailed geologic investi- 

 gation. The investigation should cover all the region from Azua westward 

 to Sierra Martin Garcia and northwestward to the hills around Las Yayas, 

 and structural studies should be made where outcrops are sufficiently 

 numerous. All of Enriquillo Basin is worthy of careful attention. Search 

 for oil seepages should be made east of Duverge and also from Neiba east- 

 ward. The triangular area southeast of the limestone slopes of the Sierra 

 de Neiba, north of Laguna Rincon, and west of Rio Yaque appears to 

 deserve most careful attention. 



San Juan Valley is so largely covered with the gravel of the Las Matas 

 formation that the folded beds beneath it can be studied at only a few 

 places. The exposure along Rio Yaque, near the east end of the San Juan 

 Valley, consist almost entirely of coarse sandy materials of no promise as 

 possible containers of oil. An examination should be made of the western 

 part of this valley, near the Haitian border, where there are outcrops of 

 lignite, possibly of Miocene age. 



