NORTHWESTERN PANGASINAN. 267 
Zambales Mountains and their general absence naturally led to 
such a belief. 
Limestones have been found on the east side of the central 
plain of Luzon at Montalban and have been referred to the 
Miocene by Smith. Adams states that at Montalban, limestone 
and conglomerate are found toward the base of the series and 
- are followed by shales, tuffaceous beds, and sandstones; these in 
turn are followed by limestone and variable clastic beds. This 
- upper series appears similar to the formation in northwestern 
Pangasinan, and a corellation is indicated. It is to be noted that 
the extensive metamorphism of the Montalban beds is a point of 
contrast, and has resulted from the intense dynamic and igneous 
activities manifested along the west flank of the Hastern Cor- 
dillera. 
Tuffs—The sedimentaries, as noted, are of tuffaceous nature. 
However, they are distinctly different from the great tuff beds 
so characteristic of the coeval strata (the great Taal tuff) around 
Manila. The Manila beds consist almost entirely of volcanic 
~ ejecta, and the coarse fragmental character of the deposit is 
highly characteristic. 'The Pangasinan beds are of a more sedi- 
mentary nature, with admixtures of exceedingly fine scoriaceous 
material. 
‘A study of the Zambales Mountains indicates that, during the 
period in which the Pangasinan sediments were being laid down, 
the voleanic activity of the range was confined to the central or 
southern portions. Owing to the distance, the ejecta, with the 
exception of the finer particles, could scarcely travel into the 
area. If the heavier particles had been carried northward by 
sea-currents, they would have lost much of their true character 
before final deposition: 
It is probable that Mount San Isidro was active before the 
os deposition of the sedimentaries now exposed by uplift. The 
aerial ejecta from these eruptions have either been eroded or 
else concealed by the later sedimentation. 
In Tarlac Province, some 75 kilometers south of the area, an- 
desitic tuffs are found on the east flank of the Zambales Range. 
- These tuffs are water-laid, stratified, soft, gray in color, and 
fragmental in texture. Hornblende crystals are visible to the 
eye, and under the microscope the glassy groundmass is seen to. 
contain numerous fragments of hornblende, tremolite, plagioclase, 
and magnetite. On the other side of the range, opposite this 
place, the tuffaceous marl mentioned on page 265 is found. 
