22 SMITH. 



the central line of the vallej'; these are along the sides, just as are 

 usually found along the sides of glaciers. 



Three distinct stages are to be noted in the history of the valley: 



o. The erosion of the broad valley; 

 6. The filling of the broad valley; 

 c. The engorging of the Aglao River. 



The first stage was that of normal erosion and began immediately 

 as this area rose from the sea. The second points to submergence or 

 sinking of the land mass and cessation of erosion. The third marks 

 reelevation of the land and quickening of the streams, so that they could 

 again begin to cut. 



It has occurred to me that very possibl}' ' when this region suljsided, 

 a tidal bore may have passed in and out of this valley and thus have 

 spread the immense bowlders over the floor as we now find them. (Plate 

 II.) 



Plates III and IV are two photograi^hs showing some interesting 

 topographic features along the route. The formation is presumably the 

 same as that composing Mount Pinatubo. However, as we had not 

 time to examine the rocks ver}^ far from the trail, I shall not go any 

 further into the discussion in this preliminary notice. 



At about 440 meters' elevation the steep climb to the summit of 

 Mount Pinatubo begins. The slopes from this elevation on to about 

 1,525 meters are quite bare and covered with small bowlders, but I saw 

 no sign of volcanic ash, nor any of the usual indications of volcanic 

 activity. Plate V shows this slope material at close range. 



There is a small, conical peak to the right and the rear which is the 

 highest point on Mount Pinatubo and of the whole range between Zam- 

 bales and Pampanga. We reached the high point to the left, 1,705 

 meters aneroid reading, as the N"egrito guide said this was the higher 

 point, and then found a canon of great depth and width cutting us off. 

 As our rations vrere running short, we were forced to forego the ad- 

 ditional descent and climb. "We would not have gained much if we had 

 undertaken the ascent, as the formation is undoubtedly the same on the 

 two peaks. We could see that with a glass. Plate VI, taken from an 

 elevation of 1,500 meters, ^rill give some idea of the view toward the 

 west over the route we came. 



The Pinatubo rock is a feldspar porphja-y. On weathered surfaces 

 it is a dirty gray, giving a pepper and salt effect. On the fresh surfaces 

 it is seen to be made up of idiomorphic crystals of glassy feldspar, or 

 plagioclase, varying in length from 1 or 2 to 15 millimiters. The black 

 mineral is usually a well-crystallized hornblende. The matrix is grayish 

 to yellow. The rock is not firm so that it easily weathere. The 

 hornblendes are invariably much smaller than the plagioclases. It is this 



