20, 1 Schenck: Drainage Control by Jointing in Angat 59 
6. That Angat River meanders to a very large extent and 
bears a superficial resemblance to a rejuvenated old-age stream 
cannot be gainsaid, though it should be pointed out that the 
elbow bends made by the river are not true old-age meanders, 
while the apparent uniform level of hilltops is due merely to the 
removing of burden from the top of a lava flow and the smooth- 
ing off of the original surface, and therefore the accordance of 
tops is not indicative of a peneplain surface. This, nevertheless, 
is not due to base-leveling during an earlier erosional cycle, but 
as evidence gained in the field indicates is due to three principal 
causes; namely, jointing, difference in hardness of rock, and 
faulting. 
The major systems of jointing seem to be northeast—south- 
west and northwest—southeast with minor north-south and east-— 
west ones, but no reliable general inclinations of the systems 
were observed, nor could the spacing be determined in so. short 
a time. The joints are frequently stained by iron oxide and, 
at places, are very definite. Ickis! found that the jointing of 
the andesite in Agos River from Infanta as far west as Macadata 
was about north 75° east, with a dip of 75° to the southeast, and 
that there are also joints that strike nearly at right angles to 
these and dip steeply to the northeast. The same observer also 
records joints striking north 20° west to north 70° east. The 
joint system in the vicinity of Paila, as noted by the present 
writer, varies from north 20° west to north 40° west, and at 
right angles thereto. Near Papaya, the major jointing appears 
to be north 50° east to north 60° east. At the head of a creek 
near Paila, a good north 35° west joint was noted, while in a 
creek near Metropolitan Dam Site 2 there is a good example of 
the northeast joint system. Below Dam Site 1, the river turns 
Sharply north 30° west after cutting a northeast box cafion 
through a hard, silicified dike.2 Other examples of this feature 
might be pointed out, and the writer believes that the main 
drainage is roughly parallel to the major systems of jointing 
and is largely controlled by them. 
The second cause of the apparent old-age drainage of Angat 
River is difference in hardness of rock. Incipient stream cap- 
*Ickis, H. M., A geological reconnaissance from Infanta, Tayabas, to 
Tanay, Rizal, Philip. Journ. Sci. § A 4 (1909) 483-487. 
*This detail does not show on the map presented herewith, because the 
map is more or less generalized. 
