Islands of Cebú and Negros. These disturbances were accompanied by much faulting, and it is believed by some metamorphism. Intrusions and extrusions of igneous rock seem to have accompanied this upheaval, but no satisfactory study has yet been made of the phenomena, good exposures being rare.

During the remainder of the Tertiary the Islands appear to have been above water. Miocene and Pliocene strata have not been detected with certainty, though some traces of such beds will probably be discovered in future investigations. Near Joló were found strata which appeared to be younger than Eocene and older than the recent period. In the main the area of the Philippines was probably continental, and there is zoölogical evidence of a land connection with the Asiatic continent, probably by way of Borneo, during the middle Tertiary. This connection did not continue to the close of the Tertiary, however, and to its rupture is ascribable the extraordinary peculiarities of animal life in the Philippines, evolution having been there left to take its own course undisturbed by invasions.

The subsidence which cut off immigration of the lower animals continued, seemingly, till somewhere about the close of the Tertiary, and long after Homo sapiens had made his appearance in the Malay Archipelago. This group also was very probably already inhabited during the Pliocene, possibly by the ancestors of the Negritos. This is a question which requires careful investigation, for in the opinion of the late O. C. Marsh the Philippine Archipelago is likely to have been one of the earliest haunts of the human species.

When the elevation was at its minimum the Archipelago was reduced to a group of small, hilly islets, four of which existed within the area now occupied by the Island of Luzón. Cebú was almost completely submerged.

At or before the period of maximum subsidence began a series of eruptions which has not yet closed. Mayón Volcano, in southern Luzón, had a violent eruption in 1897. The work done in fusing lavas and ejecting ash is probably a manifestation of the energy in the mighty earth throes which bring about regional upheavals with incidental subsidences. The earlier of the eruptions under discussion were largely submarine, and vast additions were made to the superficial material of the Archipelago by these outflows, especially in the central and southern parts of Luzón. The ejecta include andesites, rhyolites, basalts, and probably other lesscommon rock species.

The period of upheaval, once initiated, does not seem to have been interrupted by any era of subsidence, and the modern coral reefs give evidence that it is still in progress. It is said that uplifts accompanying earthquakes have actually been observed by the Spaniards, and the earthquakes themselves are spasmodic jars in the process of elevation. The

elevation has not been, properly speaking, catastrophic, however, for the tremors which may wreck a cathedral are insignificant from a terrestrial standpoint. On the whole, the uplift has been very gradual, so that even building outward into deeper water as his old home was raised too high for his welfare. In this way nearly the whole of Cebú, to a height of over 2,000 feet, has been covered with a nearly continuous sheet of coral, which can be followed seaward into living reefs. Much of Negros has been clothed with a similar mantle. On a small scale, also, off the coasts of these Islands, and particularly about Mactan, reefs can still be studied in every stage of upheaval, all those portions being dead which are exposed to the air even at the lowest tides. In southern Luzón and to the northward of Lingayen Bay similar phenomena can be observed.

Although upheaval does not appear at any time since the close of the Tertiary to have given way to subsidence, there have been repeated pauses in the uplifting process. On exposed coasts these pauses are marked by benches eaten into the land by the action of the waves. Thus the southern ends of Cebú and Bohol are terraced from top to bottom, each terrace being an old bench cut out of the rock mass by stormy seas. Pauses in the uplifting process are also marked by a rude stratification of the corals. Even in the interior of the islands terraces indicative of uplifts are frequently visible. Some of them represent base levels of erosions, others are ancient coral reefs which have been checked in their upward growth by reaching the surface of the water. In short, terraces constitute one of the most prominent topographical features of the Archipelago.

The slowness of the uplift is emphasized by the stupendous accumulation of coral in these Islands. Coral is, of course, mainly composed of calcium carbonate, and this is formed by the coral polyp from the lime salts dissolved in the sea. Now the sea contains a very minute proportion of lime salts (chiefly the sulphate of gypsum), say a tenth of 1 per cent, and corals are necessarily of slow growth, because of the scantiness of the material with which they build. The sheets of coral on uplifted areas seem to be of nearly uniform thickness, approximating 100 feet. This is explicable from the habits of the coral animal, which does not grow at a greater depth than fifteen or twenty fathoms. Unlike merely sedimentary strata, the coral follows the topography of the rising surface along a contour of which it grew. Where muddy waters or frequent eruptions befoul the sea there are no coral reefs.

When the uplift began, say ten or twelve thousand years ago, the island shores were steep and the sea about them relatively deep, so that an upheaval of 100 feet added but little to the area of the Islands. As the amount of uplift increased to something approaching the mean depth of the circumambient sea the area of the Islands increased in a far greater ratio to the increment of upheaval. The last rise of 100 feet has rescued from the sea the most valuable part of the Archipelago. Examination of

the charts will show that a fresh rise of 100 feet would add a further area, which, though important, would be less so than the actual lowlands of the Philippines. The plateau on which the Islands stand is now mostly above sea level.

Area has also been added to the land by the formation of deltas at the mouths of rivers, a process which has been greatly assisted by the mangrove trees and the nipa palms. These grow in the water in all favorable situations, and hold back the solid contents of the streams, adding their own debris to the accumulation. Along the eastern shore of Manila Bay the so-called "estero" or "bayou" country consists of the confluent deltas of the various rivers flowing into the bay.

To the eastward of the estero country the ground passed over by General MacArthur's army from Manila to San Fernando consists of low, base-level terraces, all more or less dissected by water courses. These almost always have somewhat high and steep banks. They are, in fact, engorged, as is characteristically the case in a country undergoing upheaval; for upheaval increases the potential energy of the flowing water and leads to the erosion of the stream beds.

Many of the volcanoes in the Philippines have ejected ash or lava recently, or since the occupation of the country by the Spaniards. Many other cones are plainly volcanic of no ancient date. Beginning at the south, there is at the southern end of Mindanao a group of volcanoes, none of which is known to have been in eruption since January 4, 1641. On that date there was a disturbance in the Philippines which extended far and wide. It is alleged that three outbursts took place on this day in different portions of the Archipelago, accompanied by earthquakes, which were also felt in Cochin China and Cambogia. A Spanish squadron was off the south coast of Mindanao at the time and some of the ships were almost overwhelmed by volcanic ash.

The second eruption of January 4, 1641, is described as occurring near Joló. The report states: "And although, at the time, the darkness and atmospheric disturbance were so great that the people of Joló could not perceive whence came the stuff which fell from heaven upon them, yet when it became light it was observed that at the same time when the volcano burst forth at Sanguil, Mindanao, the elements there had also become excited, and that a second volcano had opened on a small island which lies opposite the bar of the chief river of Joló, where lies our military station. The crater of this volcano is still open." Semper and Jagor are of the opinion that such an eruption really took place, but no further outbreak is known to have occurred there, and it is not known that the remains of the crater have been described.

The third eruption on that same January 4 took place from what was called "a water volcano" by the agent of the Archipelago. The descrip

tion makes it clear that by this term he had no intention of indicating thermal phenomena, but merely an outbreak of water accompanying what he himself called a frightful earthquake. This took place in Luzón among the Igorrotes. Three hills and several villages are said to have been thrown into the air in fragments. This locality is supposed to have been Mount Santo Tomás, or Tonglon, some 15 miles from Aringay, in the Province of Unión.

A group of volcanic cones exists a little to the northward of the Bay of Sarangani. They are extinct or dormant, so far as known. Mount Apo is the highest mountain in the Philippine Archipelago. It was ascended in 1880 by Mr. Montano and Governor Joaquín Rajal, who found the altitude to be 3,143 meters, or 10,311 feet, and in 1882 by Messrs. A. Schadenberg and O. Koch, who determined the height at 3,280 meters, equal to 10,761 feet. The cone is covered from about the 7,500foot contour to the summit by a mantle of sulphur. An enormous crevasse in the flank of the mountain emits jets of sulphurous acid, which escape with a strident roar. Though Apo is well known to be active, there is said to be no record of its eruptions.

On the Island of Negros are two volcanic vents. One of these is a small affair, at the southern end of the island, some 10 miles from Dumaguete on the southeastern slope of the Cuernos de Negros. The volcano of Canlaon is in the central range of the island of which it forms a culminating point. It is visible from near Iloilo, and can be seen from vessels cruising on the eastern side of Cebú. It is a very impressive spectacle, for, in addition to the picturesque form of the cone, steam is always pouring from at least two vents at the summit.

According to Mr. Semper, extinct volcanoes exist in nearly all of the islands. In the Island of Leyte are two volcanic vents from which much sulphur has been gathered. The Island of Biliran is also well known for its sulphur deposits, which are the best in the Islands. In Panay a few warm springs seem to be the only present manifestations of volcanic activity. The southwestern portion of Luzón is famous for its volcanoes, both active and extinct. Of these the most southerly is Bulusán and its shape is strikingly like that of Vesuvius.

Mayón, or the volcano of Albay, is, next to Taal, the most famous Philippine volcano. It is possibly the most symetrically beautiful volcanic cone in the world and at times its crater is almost infinitesimal. It has had a vast number of eruptions and there are recorded details of some twenty-seven, extending from 1616 to 1897. Some have been very destructive, as in 1814 about 1,200 lives were lost.

The Taal Volcano is a very peculiar one and is readily accessible from Manila. It lies on a small volcanic island in the Lake of Bombón. It has a relatively large central crater and several smaller extinct ones.

The main crater is nearly round and over a mile in diameter. Within its irregular rim are two hot pools, known respectively as the yellow and the green lake, and a little active cone about 50 feet in height from which escape steam and sulphurous gas. Taal has had some violent eruptions since the beginning of the Spanish occupation, the worst being in 1754. It consisted of fragmental ejecta, but these were sufficient to destroy four villages lying about the lake. This ash, says Semper, has now indurated and a new growth of bamboo and palms has sprung up around the projecting ruins. The eruption began, according to Bencuhillo, on May 15, and continued with intervals till December 1, when it ceased and a typhoon followed lasting two days, destroying all the volcano had left. In the Tropics nature has wonderful powers of recuperation. "In spite of the terrible lessons of the last century," comments Centeno, "all of these localities have been repopulated. Their fertility, their surpassingly beautiful topographical situation, and their unimprovable healthfulness charm the people into a prompt forgetfulness of past disasters. No great eruption has occurred since 1754. In 1808 and 1873 there were outbreaks, but the damage seems to have been confined to the island itself."

Mount Arayat is a striking object, even from Manila Bay, 50 miles distant, looming up over an extensive plain in solitary grandeur. The merest glance is sufficient to show that it is a "monadnock" and in all probability of volcanic origin. There are two peaks, of which but one is visible from the south. It is densely wooded and shows no crater, and an examination of its structure shows it must have been extinct for a long time.

The remaining volcanic mountains of the Archipelago lie in one group at its northern end. In 1856 a new volcano made its appearance not far from Camaguín, at the Didica reefs of the Farallones. It appeared in September or October, 1856, between two rocks well known to the natives, at first as a column of "smoke." No earthquake attended its first appearance, but in 1857 it underwent a violent eruption attended by earthquakes. From that time to 1860 the volcano was constantly active and in four years had reached a height of 700 feet.

So large a portion of the Philippines consists of volcanic rock as to make it manifest that there must be in the Archipelago a considerable number of volcanic belts. Such zones form one of the most prominent features of Malaysia as a whole, and the volcanic structure of the Philippines must bear an interesting relation to that of the entire region. The Nicobar Islands, Sumatra, Java, and the little Sunda Group lie along the edge of a vast submarine precipice, or, in other words, at the very abrupt limit of the continental plateau. Some of the most active volcanoes of the world are here. Papandayang, in West