248 GEOLOGICAL RECONNAISSANCE OF THE DOMINICAN REPUBLIC. 



A specimen of tuffaceous limestone from an unlimited source on the 

 south shore of Samana Bay near Punta de la Boca del Infierno, Samana 

 Province, was tested for use in waterbound macadam road and concrete 

 construction with the following results: 



Specific gravity 3 . 49 



Weight per cubic foot, in pounds 155 



Percentage of water absorbed per cubic foot 1.94 



Percentage of wear 11.2 



French coefficient of wear 3.6 



A specimen of sand-clay found in large quantity on the beach 3 kilo- 

 meters east of Sanchez, Samana Peninsula and Province, was examined 

 for use in concrete with the results shown below. The sample consisted 

 essentially of angular grains of quartz and kaolinized orthoclase with some 

 ferruginous clay. 



Mechanical analysis of sand. Per cent. 



Retained on one-fourth-inch screen 0.0 



Passing one-fourth inch, retained on 10-inch mesh 0.5 



Passing 10, retained on 20-inch mesh 0.5 



Passing 20, retained on 30-inch mesh 3.0 



Passing 30, retained on 40-inch mesh 11.0 



Passing 40, retained on 50-inch mesh 17.0 



Passing 50, retained on 80-inch mesh 36.5 



Passing 80, retained on 100-inch mesh 7.0 



Passing 100, retained on 200-inch mesh 0.5 



Passing 200 24.0 



Loss by washing (silt and clay) 12.5 per cent. 



100.0 



The value of the sand for use in cement was compared with that of 

 standard Ottawa sand by tests of the tensile strength of three specimens of 

 cement-sand briquets made of each of these two sands. The briquets 

 consisted of three parts of sand and 1 part of cement and weighed less 

 than 10 pounds each. They were tested 28 days after manufacture, with 

 the following results : 



Tensile strength, in pounds, per square inch of sample briquets. 



Ratio of strength of Sanchez sand to Ottawa sand, 65.7 per cent. 



