ECONOMIC GEOLOGY. 245 



places. Much of the gypsum is mixed with green clay or shale, but con- 

 siderable pure or nearly pure gypsum can be found. Gypsum may be seen 

 in Miocene strata at many other places, but only in the Cerros de Sal is it 

 known to occur in quantities large enough to be of any possible commercial 

 value. 



OTHER SALTS. 



Nitrate is reported to occur in the mountains on both sides of the Enri- 

 quillo Basin. A sample taken near Duverge that was supposed to contain 

 nitrate was examined in the chemical laboratory of the United States 

 Geological Survey and was found to consist of impure limestone free from 

 nitrate. Similar rock near Duverge contains thin veinlets of common 

 salt, which probably furnished the foundation for the supposition. The 

 samples of this material collected were lost in transit, so that it is impossible 

 to state whether it contains any nitrate, but even if it does the quantity 

 is apparently insufficient to be of commercial value. Potassium occurs 

 in small amount in the salt of Cerros de Sal and is rumored to have been 

 found elsewhere, but so far as known nowhere in commercial quantity. 



BUILDING STONE. 



Rock suitable for building stone is found at many places in the Republic, 

 though much of it is now too inaccessible to be used. The principal rock 

 so far used for building is the so-called "coast limestone," a marly rock 

 that is found in abundance at many places along the coast. It is soft 

 when quarried and is easily worked, but it hardens somewhat on exposure. 

 The old Spanish buildings, which are still well preserved, are built of 

 this rock. Though it does not possess much architectural beauty it is 

 accessible, is cheaply quarried, and is easily worked. Some of the harder 

 limestones of Tertiary age in the interior are better building stone, but 

 with the present lack of transportation facilities they are inaccessible to 

 most of the larger towns. No marble suitable for building stone is knuwu 

 in the Republic. Some of the granitic rocks of the basal complex would 

 make handsome building material. In many outcrops the jointing is 

 spaced widely enough for dimension stone of good size to be easily quarried, 

 but all these outcrops are too far from large towns to be of value at present. 



ROCK FOR CONCRETE. 



Rock of excellent quality for use in concrete is abundant in many locali- 

 ties. Typical trap rock— that is, fine-grained basic igneous rock— is rare 

 except at a few places in Barahona Province, but the hard, compact lime- 

 stones of early Tertiary age are acceptable substitutes. This material is 

 sufficiently tough and breaks into the angular, sharp-edged pieces which 

 are desired in concrete construction. The outcrops of early Tertiary lime- 

 stone along the northern border of the Cordillera Central, many of which 

 have been visited and described during the present investigation, afford 



