23,6 Dicker son: Baguio Plateau 419 



the region about 6 kilometers west of Baguio, where they have 

 yielded a typical Vigo fauna. 



Two kilometers east of this place coralline limestones and 

 conglomerates rest with probable unconformity upon the strata 

 of Vigo age and upon andesite intrusive in the Vigo. These 

 limestones upon the basis of their fauna have been correlated 

 with the Malumbang formation, whose type locality is in Bondoc 

 Peninsula, Tayabas Province, Luzon. Since their deposition 

 they have been elevated, folded, and faulted. 



Resting unconformably upon marly limestone phases of the 

 Malumbang formation are the tuffs and breccias of the Baguio 

 formation, which have been considerably faulted and folded. 

 Across these various rocks, through the process of erosion in 

 a tropical region, a low-lying plain dotted with well-rounded, 

 low mountains was developed over the present site of central 

 Luzon, and the streams of the early Pleistocene wandered indif- 

 ferently across the folded and faulted tuffs and breccias of 

 the Baguio formation as well as the folded Malumbang lime- 

 stones and Vigo sandstones and shales (Plate 3). The last 

 condition is well illustrated by Trinidad River, which was devel- 

 oped upon this plain and is now well intrenched in the vicinity 

 of Trinidad. After the development of this surface, the whole 

 region was elevated. The elevation was accompanied by some 

 faulting, and movements along these lines of weakness have 

 continued to the present time. The faulting is well shown by 

 the raising of such great masses as Santo Tomas above the 

 general level of the plateau. The faulting aided the enor- 

 mous erosion of the typhoon season which has almost completely 

 swept away the old Pleistocene surface from vast areas, leav- 

 ing a region that is now at the typical stage of early maturity. 

 Only the Baguio remnant exists in the near vicinity, but farther 

 northeast, at Sagada, a similar plateau is reported, and a small 

 residual is found at Pauai (Haight's place), 54 kilometers north 

 of Baguio, and at Mount Data. Dr. W. D. Smith, who recently 

 visited this noted mountain, describes it, in litt., as follows : 



Mount Data.— Mount Data is a high block mountain (altitude, 2,650 

 meters, or 8,000 feet) made up almost entirely of beds of tuff and andesite 

 agglomerate more or less in a horizontal position standing out very 

 prominently in the landscape, marked on at least three sides by very 

 imposing fault scarps. The topographic unconformity between this phy- 

 siographic unit and that of the surrounding country is even more marked 

 than in the case of the Baguio Plateau. The mountain has never been 

 accurately mapped nor even roughly outlined. The accompanying diagram 

 is an attempt to indicate its general shape and topography as sketched 



