16 GEOLOGICAL RECONNAISSANCE OF THE DOMINICAN REPUBLIC. 



IGNEOUS ACTIVITY AND GEOLOGIC STRUCTURE. 



Although the igneous rocks and their relations to the sedimentary- 

 deposits were only superficially investigated some information was obtained 

 concerning the different kinds of rocks they include, their modes of occur- 

 rence, their areal distribution, and their geologic ages. There was igneous 

 activity in the Republic prior to Upper Cretaceous time, and it was recur- 

 rent, if not persistent, in parts of the territory until almost Recent time. 

 The igneous rocks of the Republic offer a promising field for investigation 

 and enough was discovered concerning them to guide future work. 



The most important result of the study of the geologic structure was the 

 recognition of the highly significant part — in places the dominant part — 

 played by faulting in the deformation of the rocks, and we who were engaged 

 in the field felt keen regret that the lack of good maps and the shortness of 

 the time at our disposal prevented us from studying the faults in detail. 

 In future investigations of the mineral resources of the Republic the 

 contacts of the igneous rocks and the fault systems will be among the 

 phenomena that most need attention. The faults are worthy of study 

 also because of the causal relation they may bear to the severe earthquakes 

 that afflict the Republic from time to time, as it is highly probable that 

 recurrent movement takes place along certain definite zones of fracture. 



ECONOMIC GEOLOGY. 



The object of the preliminary examination was to procure reliable 

 information on which to base plans for a careful study of the economic 

 geology of the Republic rather than to prepare a special report for publica- 

 tion, but the need of such reliable information as can be given is so obvious 

 that it is now published. Chapter IX gives the results of a reconnaissance 

 of the provinces of Azua and Barahona with particular reference to oil and 

 salt and discusses the probabilities of obtaining supplies of ground water in 

 the western part of the valley of Rio Yaque del Norte. The results of 

 several special examinations of mineral properties are given in Chapter X, 

 on the economic geology, and other information on the mineral resources 

 is there summarized. There is in the Dominican Republic no established 

 mining industry of more than local importance, and none may be developed, 

 but the evidence now at hand appears to indicate that certain tracts are 

 worthy of careful prospecting, and it is reasonable to suppose that still other 

 tracts that may deserve attention will be discovered. One of the great 

 handicaps of the Republic is its inadequate means of transportation, both 

 within its own confines and with the outside world. The means of internal 

 communication are steadily being improved, however, and as the resources 

 of the Republic gain economic importance communication with the outside 

 world may be bettered. Without cheap transportation, it scarcely need 

 be said, low-grade mineral properties cannot be operated profitably. 



