X, A, 4 Pratt: Location of Artesian Wells 237 



BEDDED VOLCANIC TUFF 



Bedded volcanic tuff is found extensively in southwestern 

 Luzon and has proved to be particularly reliable as a source 

 of artesian water. This tuff has not been indurated nor con- 

 solidated through folding processes; it is distinctly bedded and 

 generally porous, but the successive beds are varyingly fine- 

 grained, so that conditions for confining water under some pres- 

 sure are very good. Many of the wells in the bedded tuff have 

 yielded flows, and a great majority have yielded either pumping 

 or flowing water. The bedded tuff formation is, perhaps, more 

 uniformly water-bearing than any other of the Philippine 

 rock series. 



TERTIARY SEDIMENTARIES 



The Tertiary (Miocene) sedimentaries consist of shales, sand- 

 stones, conglomerates, and limestones. The formation is en- 

 countered in various parts of Luzon; it makes up nearly the 

 whole of the area of Samar ; and it is important in Leyte, Cebu, 

 Panay, and in parts of Mindanao. Coal and petroleum are found 

 only in the Tertiary sedimentaries in the Philippines, and the 

 distribution of these minerals may be used as a guide in this 

 connection. The shales and sandstones are made up in large 

 proportion of volcanic material. The series as a whole is in- 

 durated and close-grained; consequently it carries but little 

 water. Moreover the fine-grained beds retain a great deal of 

 their original salt content, and this contaminates any water 

 which is obtained from them. Only a small number of wells 

 have penetrated the sedimentary series, and only a small pro- 

 portion of these have been successful. Where this series of beds 

 constitutes the underlying formation, a serious effort should be 

 made to obtain potable waters in the surface alluvium if it 

 is available. Deep wells are to be undertaken only as a last 

 resort. 



It must be admitted that some artesian water has been obtained 

 from the sedimentary rocks, but the flows are invariably small, 

 and no eminently satisfactory wells have been drilled into the 

 formation. The sandstones and the conglomerates yield water 

 under favorable conditions, but even these rocks are too dense 

 to be of great promise. The limestone members of the series 

 are very cavernous and jointed, and water percolates through 

 them readily. The lower limestone, which is very close to the 

 base of the sedimentary series, is undoubtedly the most im- 

 portant possible source of artesian water in this formation. 



