GEOLOGIC RECONNAISSANCE OF SOUTHWESTERN LUZON. 59 



of Public Works, by the Army Engineers, and by the municipalities, and 

 it is desirable that the division of mines, when called upon, should be 

 able to supply data which will aid in the various undertakings. With 

 this purpose in mind, practical results have already been reached along 

 certain lines 1 and investigations are being carried forward which can 

 not be completed in time to contribute to this paper. 



The region studied does not contain any developed metallic resources, 

 and in the part explored it is questionable if any exist, but the value 

 of the structural materials used during the past year exceeds the present 

 output of the best developed mining districts of the Islands and the 

 value of the underground waters brought to light can hardly be estimated. 

 It is probable that the coal fields in Bulacan will soon be thoroughly 

 investigated. 



The difficulties which attend geologic explorations in the Philippines 

 even in this comparatively accessible region will not be enumerated. 

 They have been mentioned by many writers, and those who know them 

 will excuse certain of the weaknesses of this report. 



Mr. Eobert N. Clark was my field aid and traveling companion, and 

 I take this opportunity to acknowledge his valuable assistance and 

 cheerful cooperation. 



PHYSIOGRAPHIC REGIONS. 



On the index map, fig. 1, the general physiographic regions of Luzon 

 Island are outlined for the first time. It is to be regretted that these 

 regions are not well enough known to warrant description. The rectangle 

 defined by heavy lines indicates the area discussed in this report and the 

 geography of it will be seen more in detail on the accompanying geologic 

 map (folded Map 1). 



Western cordillera. — The southern portion of this region, also called 

 the cordillera of Zambales, as seen from the east, presents two gaps 

 defining two mountain masses near the end of the range. The southern 

 mass is known as the Mariveles Mountains, with Mount Mariveles having 

 an elevation of 1,419 meters. The second contains Mount JSTatib which 

 has an elevation of 1,285 meters. To the north of the second and 

 higher gap are Mount Caulaman, elevation 928 meters, and Mount 

 Dangas, elevation 938 meters. Mount Pinatubo is reached by continuing 

 about 20 kilometers beyond the limits of the geologic map. Its comb- 

 like peak, which has an elevation of 1,806 meters, is considered the 

 highest point in the cordillera. 



From the indenture of Subig Bay, on which the naval station of ' 

 Olongapo is situated, one may travel by a low gap to the wide alluvial 

 valley occupied by the Pinatuan and Santo Tomas Kivers which flow 

 into the China Sea. These features separate the Cinco Picos Mountains 



1 This Joxmxal, Sec. A (1909), 4, 455 and 463. 



