472 



ADAMS. 



GRAVELS. 



Source of materials. — The only gi'avel readily available for use in 

 Manila is that which is dredged from the Mariquina River. The gravel 

 in the Pasig has already been largely dredged out in maintaining the 

 channel of the river, and although it is partially renewed during the 

 flood season when the Mariquina gravel is brought in, it does not furnish 

 a satisfactory dredging ground. 



The Quingua gravel at Quingua is too fine. Further up the river 

 near Baliuag, the same river contains a good quality of gravel but it is not 

 accessible. 



Nature of the gravel. — The Mariquina gravel is derived principally 

 from basaltic and andesitic rocks, as has already been explained in dis- 

 cussing the sands of the stream. Many of the pebbles are partially 

 decomposed and show altered spots and "pin holes" when broken. The 

 basaltic gravels frequently have a dense texture and are friable, being 

 in many respects similar to the Talim basalt which is used in macad- 

 amizing the streets of Manila, and which has proved rather unsatisfactory 

 on account of its friability. 



Granularmetric analysis. — By sieving samples of the gravel on a series 

 of stone and gravel sieves with round openings, the percentage of the 

 different sizes in several samples hgs been determined. These analyses 

 are shown graphically by the plotted curves in the following figures and 

 they may be compared with the even grade line which is shown by the 

 broken line drawn from zero to 100 per cent on the sieve through which 

 the gravel should all pass according to the specifications. 



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C£NT'M£TEffS '\'^'^, ^ "". ^ '^ * !; 

 INCHES ,/0/JeO .JO 4S 67 100 ISO 2.2S 



DIAMETER or PARTICLES IN CENTIMETERS AND INCHES 



PiQ. 11. — Ghandlaemeteic Analysis or Maeiqcina Gbavi:l to Pass a i.s-inch Opening. 



