TWELFTH ANNUAL REPORT 



41 



their utility as a source of fuel or as a lubricant has been dis- 

 cussed. This oil is characterized by a comparatively high pro- 

 portion of volatile hydrocarbons, a paraffin base, and by being 

 free from sulphur. 



71. Ore deposits. — The principles controlling the deposition 

 of ores in the Philippines, the localization of pay streaks, the 

 alteration and enrichment in calcite-quartz-manganese deposits, 

 and the extent and probable depth of valuable deposits have 

 been studied. The results of these investigations, particularly 

 those which indicate the life of the mines, are of great practical 

 value in mining operations. 



72. Baguio mineral district. — A survey of this region has 

 shown the distribution of the various formations and their 

 relation to the topography of the country, mineral veins, types 

 of ore bodies, water-power sites, transportation, timber, non- 

 metallic deposits, and various structural features such as roads, 

 bridges, and buildings. Owing to the nature of the surface 

 formations and the climatic conditions in the highlands of Luzon, 

 there is an elaborate system of fracturing along complex systems 

 of joints, and weathering extends to very great depths. Had 

 this investigation been carried out sooner and the information 

 been available before the construction of the Benguet Road, it 

 would have been of great assistance; perhaps the road might 

 not have been located where it is at present. 



73. Black sands. — Studies of the black-sand concentrates, after 

 careful cleaning at the dredges in placer districts, show that 

 values remain which would several times pay for the cost of 

 their shipment and treatment. 



74. Petrography. — Our petrographic studies of several thou- 

 sand rocks from all kinds of formations and from all parts of the 

 Archipelago enable us to say how they are likely to behave under 

 wear and stress and to indicate what rocks are suitable materials 

 for road and other construction. By means of a petrographic 

 microscope, it is possible to approximate the composition of a 

 rock and for many purposes avoid a laborious chemical analysis. 

 It is essential to know the kinds of rocks from which soils are 

 derived in order to ascertain the potential plant food, and this 

 can often be done by petrographic study. By this means we 

 have discovered the existence of potash-bearing minerals in the 

 rocks of Aroroy district of Masbate, where we had no previous 

 knowledge of them. This information is of great importance 

 to agricultural regions. 



75. Paleontology. — In an accurate and reliable survey of eco- 

 nomic deposits in sedimentary formations, particularly in coal 



