23,5 Dicker son: Baguio Plateau 427 



of the andesitic tuff, notably the cut in Trinidad Road 0.5 kilo- 

 meter north of Baguio City Hall, are well bedded and show 

 considerable sorting, thus indicating that these deposits were 

 probably laid down in a lake or in the low, flat valleys of that 

 time. However, the road exposures near the Pines Hotel show 

 another method of deposition. Here occur large angular and 

 subangular fragments of a solid andesite embedded in finer tuffs. 

 These deposits probably represent an agglomerate formed as 

 a volcanic mud flow. The third notable phase is a very hard 

 andesitic breccia composed of angular andesite fragments vary- 

 ing from 5 to 10 centimeters in greatest dimension. 



STRATIGRAPHIC RELATIONS OF BAGUIO FORMATION TO VIGO AND MALUMBANG 



The relations between the Malumbang formation, Vigo group, 

 and the Baguio formation (as revised below) were obscure to 

 Eveland and Smith, since at Trinidad, where the formations are 

 well exposed, the contact is a fault. Also, the Malumbang- 

 Baguio contact, 100 meters north of the provincial building at 

 Trinidad, is likewise a fault. When the writer attempted to 

 map a small area in the vicinity of Mount Mirador and Tri- 

 nidad Valley in detail, it was evident at once that the Baguio 

 formation rested with marked unconformity upon Malumbang 

 limestone and the Vigo group. The small outliers of Baguio 

 formation along the Mount Mirador Road and the road to 

 Dominican Hill demonstrate this relation clearly. In tracing 

 the contact between the Malumbang limestone and the Baguio 

 formation on the west side of Trinidad Valley, the writer, ac- 

 companied by Mr. James Orbison, located several residuals of 

 the Baguio formation resting upon unconformably Malumbang 

 limestone (fig. 3). The nature of the contact near the allu- 

 vium of Trinidad Valley clearly demonstrates this relation, 

 although a portion of the contact at a point 4.8 kilometers south 

 of Trinidad is a small fault. The relations between the Baguio 

 formation and the Vigo were discovered when Doctor Smith 

 and the writer examined a fossil locality which was previously 

 located as being in the tuff of the Baguio formation, but which 

 proved upon reexamination to be a marl member of the Vigo- 

 Miocene. This marl member in the local field is associated 

 with arkosic sandstone in the vicinity of Trinidad Farm School, 

 where a characteristic Vigo fauna containing Vicarya callosa 

 has been obtained. The marl member exposed along the Na- 

 guilian Road at Campo Filipino Road, 1 kilometer west of Ba- 

 guio City Hall, yielded numerous casts of marine Pelecypoda 



