X, A, 3 Smith: Reconnaissance of Mountain Province 193 



field. The feldspars are milky white. No microscopic examina- 

 tion of the feldspar has been made. The joining in this forma- 

 tion is particularly marked. 



The diorite. — The diorite is a quartz-plagioclase-hornblende 

 variety with some orthoclase and lies on both sides of the 

 granite. Bordering the granite, and apparently in the diorite, 

 are several large quartz bodies, which will be referred to again. 

 These plutonic rocks are undoubtedly very much more extensive 

 than they appear to be, but are concealed by the overlying 

 extrusives. 



The diorite I consider to be the basal formation, although it 

 may subsequently be found to be intrusive as well. I regard the 

 granite as an intrusion of rather recent date, equivalent to 

 the late intrusion in the Paracale district farther south. 



THE EXTRUSIVES 



Von Drasche has already described the typical extrusives found 

 in this region, and I have little to add to his list. However, 

 he does not make any mention, I believe, of the occurrence of 

 dacite, a glaring white rock with small phenocrysts of clear quartz 

 in a dense, creamy white aphanitic groundmass. I found this 

 well developed near the junction of the main Cervantes trail and 

 the Sagada trail at kilometer 6, south of Bontoc. Its relation 

 to the rest of the extrusive mass, which is andesitic, is difficult to 

 make out even in the fresh cliffs along the trail. It may be an in- 

 trusive. It is not essentially different from the Corregidor rock. 



There were undoubtedly several vents from which these ex- 

 trusives issued, and one of these seems to be clearly indicated 

 in a sort of broken-down craterlike topographic feature west 

 and north of the town of Bontoc. The presence of tuff beds 

 near the town dipping away from this center seems to bear out 

 this supposition. Fig. 3 is a sketch of Bontoc and vicinity, 

 showing the relationships obtaining there. 



The list of extrusives, compiled both from von Drasche's and 

 my own observations, includes: basalt, pyroxene-andesite, horn- 

 blende-andesite, andesitic agglomerate, dacite, and tuff. 



A description *' of the extrusives in the Benguet region applies 

 essentially to the extrusive rocks farther north. 



THE SEDIMENTARIES 



The sedimentary rocks in this region include the following: 

 Limestone, marl, tuff, tuffaceous sandstone, sandstone, shale, 

 conglomerate, calcareous and siliceous sinter, and travertine. 



"Smith, W. D., This Journal, Sec. A (1907), 2, 235. 



134370 2 



