So far as our information and observations went, the whole of the Philippine Islands are of similar geological formation.  In some of the islands the volcanic rock prevails, while in others coal and the metalliferous deposits predominate.  On some of them the coal-beds form part of the cliffs along the shore; on others, copper is found in a chlorite and talcose slate.  The latter is more particularly the case with Luzon, and the same formation extends to Mindoro.  Much iron occurs on the mountains.  Thus among the (Upland) natives, who are yet unsubdued by the Spaniards, and who inhabit these mountains, it is found by them of so pure a quality that it is manufactured into swords and cleavers.  These are, occasionally, obtained by the Spaniards in their excursions into the interior against these bands.

[Tufa.] The country around Manila is composed of tufa of a light gray color, which being soft and easily worked, is employed as the common building material in the city.  It contains, sometimes, scoria and pumice, in pieces of various sizes, besides, occasionally, impressions of plants, with petrified woods.  These are confined to recent species, and include palms, etc.

This tufa forms one of the remarkable features of the volcanoes of the Philippine Islands, showing a strong contrast between them and those of the Pacific isles, which have ejected little else than lava and scoria.

Few portions of the globe seem to be so much the seat of internal fires, or to exhibit the effects of volcanic action so strongly as the Philippines.  During our visit, it was not known that any of the volcanoes were in action; but many of them were smoking, particularly that in the district of Albay, called Isaroc.  Its latest eruption was in the year 1839; but this did little damage compared with that of 1814, which covered several villages, and the country for a great distance around, with ashes.  This mountain is situated to the south-east of Manila one hundred and fifty miles, and is said to be a perfect cone, with a crater at its apex.

[Resources.] It does not appear that the islands are much affected by earth-quakes, although some have occasionally occurred that have done damage to the churches at Manila.

The coal which we have spoken of is deemed of value; it has a strong resemblance to the bituminous coal of our own country, possesses a bright lustre, and appears very free from all woody texture when fractured.  It is found associated with sandstone, which contains many fossils.  Lead and copper are reported as being very abundant; gypsum and limestone occur in some districts.  From this, it will be seen that these islands have everything in the mineral way to constitute them desirable possessions.