436 The Philippine Journal of Science 1923 



reworked material derived from the older formations was 

 sought. 



In company with Dr. Warren D. Smith, Trinidad Valley was 

 studied in detail in the last two days of May, 1922, and conclusive 

 proof concerning the development of this unique valley was 

 obtained at this time. Reference to the geologic map of this 

 vicinity brings out the fact that the western side of the valley 

 is composed of the soft incoherent f acies of the Baguio formation, 

 in striking contrast to the compact and more-resistant limestones 

 which are found on the eastern side of the valley (Plate 12, 

 fig. 1). As was pointed out above, Trinidad River cuts directly 

 across the compact, thoroughly indurated facies of the Baguio 

 formation — a tuff -breccia. This tuff -breccia has a distinctly 

 bedded appearance, with a strike about north 45° east and a dip 

 of 15° southeast, in very evident contrast to the northerly dip 

 of the coralline limestone on the east side of Trinidad Valley. 

 Doctor Smith was skeptical concerning the writer's explanation 

 of the development of the Trinidad River gorge north of the 

 capitol of Benguet Subprovince at Trinidad, so that prominent 

 hill with an elevation of 1,410 meters (4,700 feet) 1.2 kilometers 

 north of Trinidad was investigated. On the east side of this hill 

 at an elevation of 1,380 meters (4,600 feet) the writer obtained a 

 good-sized piece of Malumbang-Pliocene limestone in bowlder 

 form, and this evidence as representing Pleistocene stream gravel 

 was accepted by Doctor Smith. The hill 0.4 kilometer northwest 

 of Trinidad was next climbed, and again the writer succeeded in 

 obtaining excellent fragments of limestone at 1,395 meters (4,650 

 feet) elevation. Upon climbing the hill 30 meters higher, at 

 1,425 meters (4,750 feet) elevation, Doctor Smith began finding 

 fragments of well-rounded limestone, quartz, and andesite typical 

 of the pre-Malumbang andesite, and was then convinced that 

 Trinidad River was truly an antecedent stream intrenched in its 

 present position, and that the stream gravels represented a 

 Pleistocene formation resting unconformably upon the Baguio 

 formation at these points. 9 After this discovery, Doctor Smith 

 picked out two distinct terraces encircling the valley on the 

 east, west, and south sides, which were approximately 60 and 

 90 meters (200 and 300 feet) above the valley floor, whose eleva- 

 tion is 1,320 meters (4,400 feet). In the afternoon Doctor 

 Smith, Mr. James A. Wright, and Mr. Charles Mitchek visited 



•The 1 



