ECONOMIC GEOLOGY. 247 



Tests of samples of rock and sand-clay were made by the Bureau of 

 Public Roads, United States Department of Agriculture, with the results 

 stated below. 



A sample of crystalline limestone found in large quantity at a quarry 

 14 kilometers from Santo Domingo City, near Los Alcarrizos, Santo 

 Domingo Province, tested for use in water-bound macadam road construc- 

 tion yielded the following results : 



Specific gravity 2 29 



Weight per cubic foot (pounds) 143 



Percentage of water absorbed per cubic foot (5.01 pounds) 3 . 50 



Percentage of wear 24.0 



French coefficient of wear 1.7 



A specimen of brecciated augite andesite from road cut on Carretera 

 Duarte, about 19 kilometers north of Los Alcarrizos, Santo Domingo 

 Province, tested for road metal, gave the following results: 



Specific gravity 2 . 85 



Weight per cubic foot (pounds) 177 



Percentage of water absorbed per cubic foot 0.55 



Percentage of wear 3 5 



French coefficient of wear 11 4 



Hardness 18 7 



Toughness 11 



Mineral analysis of specimen mentioned above. 

 Essential minerals: 



Plagioclase (silicate of alumina, lime and soda). 



Augite (silicate of lime, magnesia, iron and alumina). 



Rock glass. 

 Accessory minerals: 



Pyrite (disulphide of iron). 

 Secondary minerals: 



Calcite (carbonate of lime). 



The specimen is not suitable for quantitative microscopic analysis. It is 

 a very dense, fine-grained, gray-black basaltic rock, composed essentially 

 of angular fragments of vitreous basalt firmly embedded in a greenish-gray 

 glass base. 



A specimen of crystalline limestone from a large deposit of gravel in the 

 bed of Rio del Rancho Espanol at the crossing of the Sanchez and Samana 

 road, Samana Peninsula and Province, was tested for use in waterbound 

 macadam road construction and concrete mixture with the following 

 results : 



Specific gravity 2 . 74 



Weight per cubic foot, in pounds 170 



Percentage of water absorbed per cubic foot (pounds) 0.16 



Hardness 8.5 



Toughness 6 



