MATERIALS FOR CONCRKTE CONSTRUCTION IN MANILA. 465 



have been used in building the fortifications at the entrance to tlie l)ay, 

 liut none have been Ijrought to Manila, and it is probable that they 

 will not be used here since better sands can be obtained more econouiically. 



The sands used in Manila have been of only fair quality and it was 

 the purpose of the investigation to find, if possible, one of superior 

 quality. Sand from the Tarlac Eiver at Tarlac, a railroad station situated 

 halfwaj- between Manila and Dagupan. was at one time recommended as a 

 standard sand for use in testing cements, inasmuch as it was the best 

 then known in the Philippines. An examination of the map showed 

 that the sources of the Tarlac Kiver are in the Western or Zambales 

 Cordillera and it was accordingly concluded that rivers liaving their 

 sources in these mountains and emptying into Manila Bay might carry 

 the same kind of sand. It was decided that the Orani River was the 

 most promising to' investigate and upon visiting it there was found 

 an abundance of sand similar to that of the Tarlac and of a slightly 

 better quality. The river can be entered by launches and at low tide 

 the sand can be loaded directly into barges. This sand is given the 

 name of Orani sand in this report. 



Nature of the sands. — The Pasig and Mariquina sand is a pelable sand 

 which has resulted principally from the breaking down and wearing 

 of andesite and basaltic rocks and gravels. The grains are in an ad- 

 vanced stage of decomposition and crush easily. The original rocks 

 contain A'ery little quartz and so there is not a noticeable amount of 

 quartz in the sand. The few grains which may be seen in a small sample 

 are probably mostly derived from quartz veins. 



The Quingua sand is also a pebble sand, Imt it is derived from an area 

 containing a great variety of I'ocks and many of its grains are hard and 

 it contains a noticeable amount of quartz. 



The Sangley Point sand is derived principally from basaltic rocks 

 which occur fragmentally in the tuff formation which laorders Manila 

 Eay. The grains are in an advanced stage of deconipiositiou and are 

 readily crushed. In addition to the basaltic material many minute shells 

 and fragments of larger ones are p)resent. 



The Orani sand is composed largely of clear sharp grains but little 

 Tounded. It is clean and sharp and produces a decided squeak when 

 grasped in, the hand. The clear grains are readily mistaken for quartz 

 but in reality are plagioclase feldspars which have a similar hardness and 

 specific gravity. The remaining minerals which it contains are pebbles 

 and fragments of various igneous rocks. There are a few soft gravels 

 of light sj)ecific gravity found with the sand but they are not more 

 numerous than similar objectionable elements in the other sands. 



Granularmetric analysis. — For finding the percentage of the different 

 sized grains which constitute the sands, a series of sieves was obtained 

 and the sizes of their meshes carefully calibrated. The analyses made 

 bj' sieving the sands arc illustrated graphically in the accompanying 



