338 SMITH. 



not an uncommon thing for wells to be sunk apparently without the 

 slightest regard to the geology of the district wherein the well is located. 

 I know of several cases like this, one where a well site was selected by 

 means of the divining rod and later had to be abandoned; a second well 

 was drilled for twenty-two months in the basal igneous complex; a third 

 tapped a stratum which outcropped a short distance away in salt water. 

 However, such mistakes are not characteristic of the Philippines, for the 

 Bureau of Public Works has been particularly successful in its well work. 

 Although this organization has drilled wells in many parts of the 

 Archipelago, it has met with its greatest success in the central plain of 

 Luzon where artesian conditions are most favorable; that is, where 

 alternating tuff and sandy strata with intercalated layers of clay afford 

 good water passages. Many of these wells do not exceed 100 meters in 

 depth and yield a good supply of potable water. 



Some of the conditions favorable for the sinking of successful wells may 

 be enumerated as follows : 



1. A porous stratum (preferably a sandstone) with impervious strata 

 (clay) above and below, flexed into a syncline or monocline and out- 

 cropping in a more elevated and rainy region. 



2. Porous volcanic material, ash or tuff, overlain by impervious 

 material. 



3. Porous volcanic material near a coast fringed with coral reefs 

 (ponding). 



The conditions are best fulfilled in the piedmont areas where moder- 

 ately deep wells tap the coal measure sandstone lying on the flanks of the 

 eordilleras, or in the Manila tuff formation. 



Abella y Casariego, Enrique. Memoria acerca de los criaderos aurlferos del 



segundo departamento de Mindanao, Misamis. Bol. de la Com. del Mapa 



geol. de Espana, Madrid, Tello (1879), 8°, 49 pp., 5 pis. 

 Idem. Itineraries geologicos. Observaciones tomadas al paso en los viajes he- 



elios a las eomarcas auriferas de Misamis. Bol. de la Com. del Mapa geol. 



de Espana (1879), No. 6, 65-81, 1 map. 

 Idem. Terremotos de Nueva Vizcaya (Filipinas) en 1881, etc. Madrid, Tello 



(1884), 8°, 31 pp., 1 map. 

 Idem. La Isla de Biliran (Filipinas) y sus azufrales. Madrid, Tello (1884), 



8°, 11 pp., 1 pi. (map). Also in Bol. de la Com. del Mapa geol. de Espana 



(1884), No. 11. 

 Idem. El Mayon 6 Volcan de Albay (Filipinas). Madrid, Tello (1885), 8°, 



23 pp., 2 pis. Also in Bol. de la Com. del Mapa geol. de Espana (1884), 



No. 11. 



2S These are taken from a complete bibliography being prepared by Mr. Henry 

 G. Ferguson. • 



