540 PHILIPPINES. 
there were numerous pebbles of talcose rock and slate, syenite, horn- 
blende slate, and quartz, either compact or slaty. 
From these facts we learn that the volcanoes are but a subordinate 
part of the group. 
The trends of the islands and the rectangular intersections of two 
systems are worthy of our attention. Thus, the body of Luzon is at 
right angles with the south extremity ; Palawan is at right angles 
nearly with Mindoro; Panay and Negros with the south extremity of 
Luzon; the eastern part of Mindanao, with the western part. The 
seeming exceptions to the rule are nearly all found to harmonize with 
it when we observe the curving eastern outline of the group, and con- 
sider the changes of direction in the transverse trend requisite to pre- 
serve this rectangularity. At the same time we should remember that 
there is a tendency to curves in the latter trend also, as shown in the 
Sooloo Islands tailing off from Western Mindanao. 
LUZON. 
The island of Luzon has nearly the shape of a boot, lying north and 
south, with the foot turned eastward. ‘The body is about three 
hundred and fifty miles long, and the southern extremity or foot two 
hundred and fifty miles. In our approach to it, we first made the west- 
ern cape, where we observed in the distance a range of high mountains, 
with rather even slopes and undulating outline, and low flat shores 
bounding apparently extensive plains. As we neared Manilla, several 
isolated heights came in view, which had the appearance of volcanic 
cones, and just north of the bay, one of these high elevations, with long 
slopes and broken summit, still retained small craters upon its sides, 
although the declivities were deeply worn by denudation. Another 
peak farther to the north presented similar features. The even declivi- 
ties slope at an angle of about twelve degrees, gradually diminishing 
downward, and becoming nearly a level plain at foot. The large har- 
bour of Manilla is bounded by a low level country, which in the dis- 
tance to the westward rises into mountains, mostly two or three 
thousand feet high; and one flat-topped cone of full six thousand 
feet shows itself in clear weather. On the north, the only point seen 
from our anchorage, rising above the flat shores, was the cone called 
Mount de Arayat, which is thirty miles distant, and over five thousand 
feet in altitude. 
