Agno rises in the mountains on the north border, flows south,
south-west and north-west, and discharges through several channels
into the Gulf of Lingayén. Each of these has a great number of
small tributaries, and along the coast of this lowland basin are
many small tide water streams. The Pasig is a short but commercially
important stream connecting Laguna de Bay with Manila Bay.
The Rio Bícol, which rises in Lake Bato and flows N.N.W. into San
Miguel Bay, is the principal river of south Luzon. Samar, Panay,
Negros, Leyte, Bohol and Cebú are drained by many streams, and a
few of those in Samar, Panay and Negros are of considerable size.
In the lowland basin of central Luzon, 6 m. inland from Manila Bay, is Laguna de Bay, the largest body of fresh water in the Philippines. It is 32 m. long from north-west to south-east and its coast-line, broken on the north by two hilly peninsulas, is 108 m. long. Lake Taal, a few miles south-west of Laguna de Bay, occupies the crater of a great volcano. It is 17½ m. long and 12 m. wide. The country rises gently to it on all sides, and on an island near its centre is the active volcano of Taal, 1050 ft. high. In north Luzon is Lake Cagayán. In Mindanao there are lakes Lanao, Liguasan and Buluan in the west-central portion and lakes Mainit, Pinaya, Dagun, Sadocum and Linao in the valley of the Agusan. There are small lakes in some of the other islands.
Geology—The Philippines appear to be the remnants of a somewhat complex system of mountain arcs, which from their similarity of form and direction seem to be in some way connected with the mountain ranges of Annam. The oldest rocks exposed are gneiss, talc-schist and serpentine, with intrusive masses of gabbro and diabase. These are overlaid by a limestone, upon which rests conformably a series of sandstones with coal seams. The age of these beds is unknown. In some of the islands nummulitic limestone (Eocene) occurs. Coral limestones, probably of Middle Tertiary age, are also found, sometimes 4000 ft. above the sea, and marine deposits of a very late geological period occur near the coast and in the low-lying depressions. Volcanic rocks of modern date cover extensive areas, especially in the southern part of Luzon and in Mindanao. In Luzon trachytic tuffs are sometimes interstratified with nummulitic limestone, thus showing that the eruptions had already begun In the Eocene period.
Volcanoes and Earthquakes.—There are twelve active volcanoes in the archipelago. They are Babuyán Claro, Camiguín de Babuyanes and Didicas in the Babuyanes Islands off the north coast of Luzon; Cagua or Caua in north Luzon; Taal, Mayón and Bulusan in south Luzon, Canlaon and Magasó in Negros; Camiguín de Mindanao in the Island of Camiguín, off the north coast of Mindanao; and Apo and Calayo in Mindanao. Only a few eruptions have been recorded of any of these, however, except Taal and Mayón, and there has been no great eruption of Taal since 1754. But there were 26 eruptions of Mayón in the 19th century, and those of 1814 and 1897 were of great violence. That of 1897 began practically without warning on the 23rd of June, became alarming on the 24th and destructive on the 25th, and ceased on the 30th. Streams of lava completely destroyed several villages and injured others, as well as the town of San Fernando. The lava flow extended more than 7 m. eastward, and a rain of ashes extended 100 m. to the east and 75 m. to the west. There are eight other volcanoes, which although extinct or dormant have well-preserved cones. They are Aráyat, Banájao, San Cristóbal, Isarog and Malinao in south Luzon, and Macaturin and Matutum in Mindanao.
Earthquakes are frequent and occasionally violent. In the seven years 1902–1908 the micro seismograph at Manila recorded 796 local earthquakes. In the 47 years ending March 1909 the various regions of the archipelago were visited by about 60 strong earthquakes; 16 of these, in ten different regions, occurred in the decade from 1890 to 1900. There were 8 in the year 1897 alone, and one of these ruined the town of Zamboanga in west Mindanao and caused considerable loss of life by falling buildings and immense sea waves. A new island appeared at this time off the coast of Borneo, near Labuan. The principal centres of disturbance are in the valley of the Agusan, in the region of Mayón volcano, in the region of, Taal volcano, on Masbate Island, and along the north shore of Luzon. The islands of Cebú, Bohol, Negros and Palawan are rarely shaken.
Fauna.—The Philippines, politically speaking, and the Philippines, zoologically speaking, are not identical areas; Balabac, Palawan and the Calamianes being characterized by the occurrence of numerous Bornean forms which are conspicuously absent from the remaining islands. Although the Philippines are commonly held to form an eastern extension of the Indo-Malayan sub-region, there is a large amount of specialization in the fauna of the islands eastward of the Palawan group. Mammals are scarce. No marsupials occur. The edentates are represented by the pangolin (Manis sp?) of the Palawan group. In the seas are found the dolphin, cachalot and dugong. Wild hogs of at least two species occur. The beautiful axis deer of Sulu has apparently been brought there by man. Red or brown deer occur in Basilan, Mindanao, Leyte, Samar and the Calamianes Islands. The number of species and their respective ranges have not been satisfactorily determined. In Masbate, Panay, Guimaras and Negros there is a dark-coloured species marked with buff spots. Deer are absent in Palawan, Tawi Tawi, Tablas, Romblon, Sibuyan and Siquijor. Humped cattle are raised on most of the islands. They are killed for their flesh, hides and horns, and little attention is paid to their milk giving properties. The water-buffalo, or caraboa, occurs in a wild state in Luzon, Mindoro, the Calamianes group, Masbate, Negros and Mindanao, but the wild herds are believed to have originated from domesticated animals. The domesticated water-buffalo is sluggish in its movements, and will not work through the heat of the day; but it is a wonderful swimmer, and makes its way through the worst quagmire with ease. It is universally used as a draught animal and beast of burden. The most interesting of the ruminants is the timarau (Bubalus mindorensis, Heude), peculiar to Mindoro. Unlike the water-buffalo, it does not bathe in water or wallow in mud. It is extremely wild, feeding by night and sleeping by day in the densest jungle. It sometimes charges the hunter without provocation, and is very dangerous when wounded. It attacks and kills the much larger wild buffalo. All attempts to domesticate it have failed. A chevrotain is found in Balabac. The house rat, introduced by man, is a common nuisance, and mice occasionally seriously damage sugar-cane and rice. Squirrels are confined to the eastern chain of islands from Basilan to Samar and to the Palawan-Calamianes group. In the southern islands there is a tiny species, the size of a mouse. Very large flying-squirrels are found in Palawan and Mindanao. Squirrel-shrews occur in the Palawan-Calamianes group, and true shrews at various points in the archipelago. Among the Carnivores are the binturong and an otter, both found in the Palawan-Calamianes group; two civet cats, which range throughout the archipelago, and a wild cat of small size, which has been found in Palawan, Panay, Negros and Luzon. Bats are very numerous, and a number of the species are peculiar to the Philippines. Galeopithecus and Tarsius range from Basilan to Samar; the former occurs also in Bohol. In spite of all that has been said to the contrary, but one species of monkey (Macacus philippinensis, Geoff.) has been discovered in the Philippines. It occurs on every island of any importance. Its flesh is occasionally eaten by the natives. Albino specimens of this monkey are not uncommon, but the pure white monkeys, not albinos, said to inhabit Mindanao, are mythical. The large fruit bats (Pteropus) occur in immense colonies, and are sometimes eaten by the natives.
Especial importance attaches to the unexpected discovery by Whitehead of a new and peculiar mammalian fauna, inhabiting a small plateau on the top of Mt Data, in north Luzon, at an altitude of more than 7000 ft. Specimens of 15 species were obtained, embracing 5 new genera (Calaemomys, Chrotomys, Rhynchomys, Batomys and Carpomys). Eight of the species were new and strikingly peculiar. Their zoological relationships are probably with Celebes and with Australia. Other discoveries include a few new squirrels and bats, and the occurrence of a lemur (Nycticebus tardigradus) in Tawi Tawi.
The islands are as rich in birds as they are poor in mammals, the total number of species recorded up to 1906 being 693, of which about one-half are peculiar to the Philippines. A study of their geographical distribution has demonstrated that the islands may be divided into fairly well-marked groups, in each of which the birds show a degree of specialization closely correlated with diversity of environment and completeness and probable duration of separation from adjacent groups. Balabac, Palawan and the Calamianes show a very strong Bornean element. Mindoro stands by itself. Luzon and the small neighbouring islands have 51 peculiar forms. A close relationship exists between the birds of the entire eastern chain of islands. Numerous genera and some families which are absent from the central islands range from Luzon to Basilan. These genera usually have distinct representative species in Luzon, Samar and Leyte, Mindanao, and in some cases in Basilan also. The greatest differences occur between Luzon and Samar and Leyte. The latter islands have 22 peculiar species.
Sulu and Tawi Tawi belong zoologically to the Philippines, but have 12 well-marked peculiar species, an many of the characteristic Mindanao-Basilan forms are lacking. Panay, Guimaras, Negros and Masbate constitute a sharply defined area, characterized not only by the occurrence of 30 peculiar species, but by the absence of important genera, and even whole families represented in the eastern islands. Most of the mammals characteristic of the latter region are lacking. It is a curious fact that Cebú stands quite by itself, although the deep channel separating it from Negros narrows at one point to about 4 m. Cebú possesses 9 striking species of birds not known to exist elsewhere, and lacks many of the characteristic forms of the central and eastern islands. The zoological position of Bohol has not been satisfactorily determined, but all existing evidence indicates that it must be grouped with Samar and Leyte.
Among the more interesting birds may be mentioned the “mound builder” (Megapodius cumingi, Dillwyn), which buries its large eggs in the soft sand along the sea beach, or under great mounds of earth and dead leaves, often at a depth of three or more feet below the surface. The young are forced to dig their way out and shift for themselves. The eggs are highly prized by the natives. The jungle fowl abounds. There are 35 species of pigeons and doves many of them most beautifully coloured and all edible. Snipe, plower, turnstones and other shore birds are abundant during
