Pe poe Nowe). te tas 
377 
The lithologic structure of Mount Mariveles shows it to be of volcanic 
origin. It is a mass composed largely of andesitic ejecta and of the 
decomposition products thereof.’ The physiographic features which 
point to its being an extinct volcano are almost as striking. Rising 
from Manila Bay on the east, from the China Sea on the south and west, 
and from the lowlands near the central part of Bataan on the north, are 
a series of prominent ridges ending in the peaks which, with their con- 
necting ridges form a nearly circular chain—the rim of the former crater 
which has an outlet to the north, by way of the Balanga River. (See 
map.) Between these peaks and just beneath the lowest point of the 
connecting ridges are the sources of the main rivers draining the 
mountain ; the latter have cut deep cafions and have established many 
branches with smaller ones. With the exception of Limay Peak, which 
will be discussed in another connection, the mountain, with its regular 
caions and ridges which begin at the base and end at the rim of the 
crater, suggests that in the past it was a more or less perfect cone, con- 
siderably higher than at present and similar to Mount Mayon, in the 
Province of Albay, Luzon. According to Becker,!® the volcanic period 
which gave rise to the earlier andesitic rocks now present in the Philtp- 
pines very probably occurred in the Post-Eocene upheaval. If Mount 
Mariveles originated at this time, then the present erosive topography of 
the mountain is no older than the length of the interval intervening 
- between the Miocene and the present date; probably it is considerably 
younger, for the voleano must have remained in activity for some time 
after its origin. At present there are no signs of volcanic activity if we 
except some hot springs near the base of the mountain at Port Mariveles. 
The condition of the mountain to-day is only one stage in the process 
of its destruction by the normal erosive forces. It is conceivable that 
its vegetative condition, because of its prominent topography of alternat- 
ing ridges and cajions, is considerably different from that of some other 
volcanic peaks on the Islands. which are in various stages of their life 
history. The youthful. Mayon, with its cone-like, little eroded topog- 
raphy, or Mount Banajao, in Tayabas Province, with a physiographic 
condition intermediate between that of Mayon and Mariveles, will show 
vegetative conditions due to factors to some extent at least dependent 
on their respective life histories. 
Lamao River Reserve.—The portion of Mount Mariveles with which 
this paper deals lies on its east slope and comprises an area of approx- 
imately 4,426 hectares. It is known as the Lamao River Reserve, and has 
*I am indebted to H. D. MecCaskey, of this Bureau, for information concerning 
the lithologic structure of the mountain. See also Becker, Geo. F. Report on 
the Geology of the Philippine Islands. Annual Report of the U. 8. Geog. Sur. 
(1901) 21, 111, 514. 
* L. c., 567, 568. 
ait cae 
