246 GEOLOGICAL RECONNAISSANCE OF THE DOMINICAN REPUBLIC. 



unlimited supplies of such material, awaiting only adequate transportation 

 facilities to be utilized. Similar rock has been described in the Sierra de 

 Monte Cristi, at the west end of the Cordillera Septentrional. Some of it 

 occurs near Puerto Plata and doubtless in other parts of the Cordillera 

 Septentrional. Large areas of limestone of this general type are found in 

 the provinces of Barahona and Azua. These areas have been partly 

 mapped on the geologic map of that region. Other sources of concrete 

 material are to be found in the great batholithic masses of granitic and 

 dioritic rocks in the Cordillera Central. Most of these are remote from 

 large towns, but almost every stream that emerges from the Cordillera 

 carries large quantities of these rocks in the form of gravel and boulders. 

 Where such stream gravels are found close to places where concrete is 

 needed they can be crushed so as to produce sharp edges and successfully 

 used. Uncrushed stream gravel is often used in concrete, but the rounded 

 smooth pebbles do not produce so strong a concrete as angular, sharp- 

 edged rock. 



ROAD METAL. 



The discovery of rock suitable for road metal is one of the great problems 

 before the engineers of the Republic, for the construction of good roads is 

 one of the improvements most needed in the island. After a system of 

 good roads is once established and adequately maintained many of the 

 other desirable improvements in industry and in the condition of the people 

 will naturally follow. The limestone and igneous rock mentioned above as 

 suitable for concrete construction would also make excellent road metal if 

 it could be economically quarried and transported to the places where it is 

 needed. The schistose limestone of Samana Peninsula and some of the 

 metamorphosed ferromagnesian rocks and of the harder sedimentary 

 rocks of the basal complex might well be utilized as road metal, but most 

 nf thpsp nrp far from the places where roads seem to be most urgently 

 needed, and the soft marly limestone of the coastal plains is therefore 

 extensively used as road metal. It is cheaply and easily obtained and has 

 fairly good binding power, but it is too soft to make really permanent roads. 

 Some of the rocks that would make excellent road metal are not very far 

 from the line of roads now under construction and are quite close to 

 places where roads will eventually have to be constructed. Perhaps some 

 plan by which these rocks could be used might be devised. If quarries 

 were established at suitable places and roads built from the quarries by 

 using the good road metal obtained there many of the difficulties now en- 

 countered in road construction would be eliminated. With good material 

 at hand the construction should proceed at a faster rate than at present. 

 The Telford type of road, so extensively used in France, has certain ad- 

 vantages where labor is cheap and the rock is soft and breaks into slabs, 

 and it might be advantageously used in some parts of the Dominican 

 Republic. 



