98 ADAMS. 



The escarpment which runs northward from Mount Gonzales along the 

 western limit of the alluvium which borders Bay Lake, and continues 

 to the west of the Mariquina Valley may owe its origin to a fault scarp 

 which has receded westward by erosion. When one studies the gap 

 between Mount Sungay and Mount Maquiling, he is impressed with the 

 fact that the country is much lower than the area to the west, and finds 

 it difficult to acount for the discontinuance of the ridge eastward from 

 Gonzales except by means of faulting. 



The general level of the country east of Gonzales Mountain and Taal 

 Lake is continued westward between the Tagay-tay ridge and Taal Lake 

 for a short distance and when viewed from Taal Lake has the appearance 

 of a terrace. (See fig. 9.) This seems to indicate that the deposition 

 of the tuff formation was continued after the elevation of the Tagay-tay 

 fault block. 



On the eastern border of the tuff area, which is indicated in a very 

 rough way on the geologic map, the deposits overlie the folded tertiary 

 formations. In this locality it is likewise difficult to decide whether the 

 tuff deposits are subaerial or water-laid and much further work must be 

 done in order to determine their full extent. The tuff is found at 



Ml. Gonzales 

 Tagiiy-tay ridfea 



Fig. 9. — Sketch Showing the Relations of Tagay-tay Ridge and the Upland 

 on the Northeast Border or Taal Lake as Seen from Lipa Point. 



levels of at least 50 meters above the sea and there is naturally some hesita- 

 tion in assuming that there has been so great an emergence as would have 

 been required to lift the tuff beds from below sea level. 



In the upland to the southeast of Pagsanjan the streams flow in deep 

 gorges in the walls of which coarse agglomerates with a matrix of tuface- 

 ous material are exposed. In places there are clear indications of bed- 

 ding and some strata of the tufaceous material are clearly water-laid. 

 The escarpment at the border of the upland east and southeast of Bay 

 Lake appears to have once been a cliff and later its base was the border 

 to Bay Lake which has since receded from it. With the elevation of 

 the area the streams of what it now the upland, cut their valle}'s deeper, 

 forming gorges and the falls caused by the resistance of the harder beds 

 of the agglomerates have gradually receded to their present jsositions. 



In this connection it is interesting to note that some tufaceous deposits 

 related to the area of basaltic eruptives in the vicinity of Antipolo appear 

 to be water-laid and contain conglomerate phases well exhibited in the 

 stream bed near the railroad bridge. 



At the gorge of the Mariquina Biver, where a dam has been built as 

 the headworks of the Manila water supply, it is apparent that the river 



