RIVER SYSTEMS 529 



/. Bicol. — This, the most important river in southeastern Luzon, rises 

 in Bato Lake and flows northwesterly through the volcanic plain at the 

 foot of Mount Isarog, emptying into San Miguel Bay. The most impor- 

 tant town on it is Nueva Caceras, which is located at the head of naviga- 

 tion for ocean-going inter-island vessels. Above this town it is navigable 

 for a considerable distance for flat-bottomed boats, especially in times of 

 high water. In the uppermost regions a unique system of transportation 

 is used, a dug-out towed by a carabao — a method due to the fact that the 

 stream is exceedingly shallow in places, while in others it is much deeper. 

 The lazy native finds it easier to be towed by his animal than to propel 

 the boat by poles, especially since the carabao can swim in the deeper 

 places and does not mire down in the shallow, muddy reaches where he 

 walks. 



g. Abra. — Rising on the flanks of Mount Data, in north-central Luzon, 

 the Abra flows west for a short distance before it turns northward — in the 

 tectonic valley to the east of and parallel to the Malaya Eange — almost as 

 far as the town of Dolores, where it turns sharply to the west. From this 

 point it proceeds in a south-of-west direction and breaks through the 

 coast range just south of Vigan. It is navigable only for rafts and dug- 

 outs. From the situation of this stream and some of its tributaries, it is 

 the opinion of the writer that the Abra is a captured stream, and that 

 formerly there was a more important watercourse of greater length which 

 followed the Abra Valley, though possibly much farther north, and that 

 it may even have debouched near Laoag, many miles to the north of 

 Vigan. A good atlas map of Luzon will show the location of most of 

 these points. 



h. Agno. — This stream also rises on the flanks of Mount Data, but 

 flows south in another structural valley and debouches onto the central 

 plain of Luzon. Due to warping of this plain, the river makes a great 

 sweep and turns to the northwest, emptying into Lingayan Gulf by way 

 of a series of smaller channels. It is practically entirely unnavigable, but 

 is worthy of consideration because of the great destruction caused when 

 it floods its banks, as happened so disastrously in the rainy season of 1911. 

 At that time almost tlie entire country from Moncada to Dagupan was 

 under water, and in places the flood rose nearly to the tops of the tele- 

 graph poles. At the same time an important new dam and irrigation 

 project which the Government was building was almost completely oblit- 

 erated. 



Lakes 



There are several different types of lakes to be found in the Philip- 

 pines. The most common are those which are little more than deepened 



