544 SOOLOO ISLANDS. 
that about the Laguna de Bay, and it is probable that they were alike 
in origin. Some islands near the entrance appear to be remains of the 
smaller subordinate craters, while the high summits of the adjoining 
country were evidently its great volcanoes. Their lofty conical form 
leaves no doubt of their volcanic origin. 
The latest volcanic eruptions of these regions appear to have been 
attended with extensive ejections of ashes and scoria. ‘This is the 
usual operation of subsiding fires. 
This volcanic portion of Luzon is remarkable for the richness of its 
soil and its luxuriant vegetation. It affords abundantly most of the 
fruits and agricultural products of the tropics. Rice, coffee, sugar- 
cane, cotton, and Manilla hemp, are the most important crops. 
The secondary deposits of Luzon are not found in the region over 
which our two days’ ramble extended. The specimens of coal exa- 
mined at Manilla were associated with a greenish gritty sandstone, 
which is said to contain fossil shells. The coal looks much lke our 
own bituminous coal. Some of the masses were eight inches thick, 
and possessed all the lustre and compactness of the ordinary Liverpool 
coal. Many of the specimens had a rough brown exterior, one-eighth 
of an inch deep, which had resulted from weathering. 
Calcareous rocks are found at Beningona north of the Laguna de 
Bay: and on the shores of this lake there are said to be limestones 
forming from recent shells. 
I was told by Sefior Roxas that a bed of coral occurs on the shores 
of Luzon, six hundred feet above the level of the sea, at Point St. 
Diego, south of Manilla. 
SOOLOO ISLANDS. 
The Sooloo Group contains about a hundred small islands. They are 
sprinkled through the sea in a line between Mindanao and the north 
of Borneo, and among them are numberless submerged coral reefs. 
Traversing these regions, we were much of the time on soundings, 
and anchored in the open sea at night. Several islands were in 
sight at once. The largest of the group, Jolo (or Sooloo,) is about 
thirty-six miles long and sixteen broad. From this size, they dwindle 
to mere points of rock. 
All the islands are volcanic, excepting some patches of coral reef. 
When off the shores of Mindanao, I counted ten or twelve distinct 
