22, i Aguilar: Waters of Angat and Montalban Rivers 47 



A high proportion of silica in the mineral content of surface waters 

 is thought by many observers to be normal only to small streams flowing 

 from crystalline siliceous rocks, and especially to those streams near 

 their sources; that is, if silica is a prominent constituent of the inorganic 

 "1? T! 1 dlSS0lved m the water of a lar &e stream, its presence must be 

 attributed to some extraneous cause, such as tropical climatic 

 in the drainage basin or abundance of organic matter in the waters. 

 Table 2.~Results of analyses and computations (station 2). 



Looking over the chemical analyses of some river waters in 

 the Philippine Islands, 4 it is apparent that high silica content 

 is a general characteristic of Philippine river waters; on the 

 other hand, analyses of various river waters in the United 

 States 5 show on the average a much lower silica content. These 

 results seem to indicate that the tropical climatic condition is 



water supplit 



4 Heise, G. W., and Behrman, A. S., Ph 

 f Science publication 11 (1918) 148-151. 

 5 Dole, R. B., U. S. Geol. Surv. Water-Supply Paper 236 (1909). 



