mountain sliding out, so that there is a great gap in the crater on one side. In spite of the great size of these mountains and the deep canyons on their slopes, they are of very recent origin. Recently Adams, who made a trip through that country, has compiled all of the various reports in a very interesting and able discussion in his "Geological Reconnaissance of Southeastern Luzon," which is found in Vol. VI, No. 6, Philippine Journal of Science. Of all the travelers through this district, Martin, the government photographer, is the only one who has brought back good photographic records. In 1909, Mr. Martin and a Franciscan Father from the town of Tobaco, made an ascent of Mount Mayon and secured fine pictures of the crater and of the country as seen from the crater. The most interesting point in connection with Mount Mayon, is, that the curve of its slope is so perfect that it can be represented by the formula for the sine curve: This was worked out by Dr. G. F. Becker of the U.S. Geological Survey, who made a geological reconnaissance of that region in 1901. An extensive population is found at the foot of these mountains, but in the higher parts there are only a few Negritos. This district is one of the finest in the Islands, from a scenic point of view, as well as agriculturally, and occasionally, as in 1900, very spectacular eruptions take place from Mount Mayon. Further south in Sorsogon is another large dissected volcanic stock called Mount Bulusan. This is very much like Mount Isarog in general appearance. THE RIVERS There is a host of rivers of all sizes in Luzon. I shall, however, refer to eleven only. The largest river is the Cagayan in the northern part of the island, the shortest, perhaps, is the Pasig, but from a human standpoint, the Pasig is by far the most important of all. The Cagayan. This river rises at about latitude 16°, and empties at Aparri, N. 18° 30'. Apart from local sinuosities it is a remarkably straight river, leading one to believe that it must follow some structural line. This river is navigable up to Ilagan, and along its banks are located the principal tobacco fields of the Islands. At Aparri considerable difficulty is experienced from the formation of bars crossing the river mouth. The insular government is spending considerable money in keeping this channel open. This stream flows in a very wide, level plain and the soil is remarkably rich. The Pampanga.-The second largest river of Luzon is the Pampanga. This river rises in the Caraballo Sur Mountains or in the "Central Knot," and flows somewhat west of south and debouches into Manila Bay, by means of a myriad of channels. This river is navigable for a long distance into the interior, and is one of the principal highways of commerce in Luzon. The Agno. The Agno river rises on the slopes of Mount Data in north central Luzon, and flows due south until it reaches the Pangasinan Plain where it turns sharply to the northwest and empties into Lingayen Gulf. This river is navigable for a short distance from its mouth, but in the mountain district is simply a roaring torrent washing along big bowlders, and is not at all navigable. This river overflowed its banks twice during 1911, flooding a large section of Pangasinan Province. The Abra.-The Abra rises also on the slopes of Mount Data, then turns abruptly to the north, flowing for 40 miles or more until it gets to the town of Dolores, where it makes another very sharp bend and flows southwest, emptying into the ocean near Vigan. This river throughout a great deal of its extent is located in a deep gorge. Very little is known of the geology along its course. The Bicol River.-The Bicol River where it rises due west of Daraga is known as the Kinali River. Thence it flows northwest along the Albay central plain, through one lake (Lake Bato) and a large swamp, finally emptying into San Miguel Bay. This river is navigable almost to Bato Lake. It very frequently overflows, and for this reason, the district through which it flows is one of the principal rice districts of the Islands. The Angat River. The Angat River is referred to here more on account of its length, than for any other reason. It rises in the Eastern Cordillera, flowing with considerable sinuosity westward, and empties into the Kingwa River which also flows across the Bulacan Delta into Manila Bay. This river is not navigable to any great extent, but at Norzagaray the river has some falls where considerable power could be obtained. The Bued River. The next river in point of size is the Bued River, which, while much shorter than the Agno, flows in the same direction, and is only mentioned here, because of its connection with the famous Benguet Road. This river is probably responsible for more damage to the works of man than any other river in Luzon. During the summer of 1911, it was the scene of a very destructive flood, which was due to a cloudburst, near Baguio. Thirty-seven inches of rain fell in twenty-four hours in Baguio. The larger part of this water flowed into the Bued River Canyon, and at the lower end, there occurred a great landslide which dammed the stream to a height of 60 feet. When this dam broke, a large portion of the lower end of the Benguet Road was washed out into the Pangasinan Plain. This road has suffered repeatedly from these floods. The Pasig River.-The Pasig is a very short river, 15 miles, very deep and of moderate width, and is the outlet of Laguna de Bay. It is important mainly because of the great volume of commerce which travels along it, and for the fact that the capital of the Archipelago is situated at its mouth. This river is tidal in its lower section, about up to Fort McKinley. From here on to the lake, it is much narrower and quite shallow in places. The river has a very treacherous current. The Paracale River.-The Paracale River is mentioned here not on account of its size, but because it is distinguished by two very important features. The most important is that it is probably the richest river of all, there having been discovered considerable stretches of rich gold placers along its course. From a physiographic point of view, it is interesting, because, in its lower portion, this river is a drowned river. It has long been known that the Camarines coast is subsiding. THE LAKES AND SWAMPS The true lakes in Luzon are first and foremost, Laguna de Bay; second, Taal Lake; third, Laguna de Canaren, Bato and Buhi, while the following, Paway, Cagayan, Pamplona, Mangabol, and Candaba are merely great swampy areas, whose size changes with the seasons. FIG. 3.-Taal Lake; Taal Volcano on low island in right background G. I. Adams, "Geologic Journal of Science, V, No. 2. In his study of the Southwestern Luzon region, Adams has discussed the two firstnamed bodies.1 Laguna de Bay is a heart-shaped body of water with two prongs of land projecting into it from the north side. It lies a short distance southeast of Manila, and is separated from Manila Bay by about 6 miles of land. Its dimensions are 25 by 28 miles. It is fairly shallow. The height above sealevel varies between 0.9 and 4.3 feet. Taal Lake. The second largest lake in Luzon is Taal Lake or Laguna de Bombon (Fig. 3). This has generally been regarded as a crater lake by such writers as von Drasche and Becker, but Adams who has perhaps given more time and study to it than any other, attributes the origin of the lake to peripheral faulting. My own opinion is that the lake has originated through (1) peripheral faulting, (2) explosion of a former and much larger volcano than now exists there, and (3) subsequent collapse of the crater area (Fig. 4). For details about this lake and volcano, I shall merely refer the reader to the three most exhaustive articles on this subject.2 THE HUMAN RESPONSE TO PHYSIOGRAPHIC CONDITIONS The relationship between man's work and physiography, has long been emphasized by many writers. Although this relationship has often been over-estimated, Reconnaissance of Southwestern Luzon," Philippine 2 G. I. Adams, op. cit.; W. E. Pratt, "Eruption of Taal Volcano," Philippine Journal of Science, VI, No. 2; D. C. Worcester, in National Geographic Magazine, 1912. |