348 SMITH. 



The Eio Grande de Mindanao 5 has its source in the mountains east of 

 Cagayan, Misamis, and flows almost due south to the southern boundary 

 of the subprovince of Bukidnon, swings west to the town of Sevilla, then 

 east again in a wide curve and then southwest; a few kilometers north 

 of Lake Liguasan it turns at right angles and flows a few degrees north 

 of east into Illana Bay. It is quite probable that the former mouth was 

 very close to Lake Liguasan and that the river has gradually grown 

 southward as it built up the delta mentioned on page 347. Meanders 

 are quite common in this river (see Plate II), there being one point near 

 Tumbao where, by taking a small canal of 50 or 75 meters in length, over 

 half an hour of travel can be saved. The banks show no rock exposures, 

 nothing but mud could be seen as far up as I followed it. The fall is 

 only about one in 5,000, as the 30-meter contour does not cross it until a 

 point 10 or 12 kilometers above the confluence of the Kabakan and 

 Pulangui is reached, or about 160 kilometers from the sea. 



It is difficult to navigate any but light, flat-bottomed craft above the 

 Kabakan. A flat-bottomed, stern-wheeled steamship drawing not over 

 2 feet should be able to ascend 80 kilometers above this point, and it 

 might reach Sevilla, were it not for Murphy's rapids, which Captain 

 Murphy describes as occurring in the vicinity of the Alanan Kiver. I 

 suspect that an outcrop of some hard, igneous rocks, like diorite, occurs 

 here. Unfortunately, the Army topographers, to my knowledge, collected 

 no geologic specimens in the course of their work in this portion of the 

 Cotabato Valley, and perhaps with good reason, for all through Minda- 

 nao traveling and packing is extremely difficult. The United States 

 Army engineers have made an excellent topographic map of a large part 

 of the Bio Grande and the region it drains, particularly that to the 

 north. The topography by Captain Murphy and his associates in this 

 region shows that the old maps were very broadly generalized, to say the 

 least, and in many instances totally wrong. There is nothing resembling 

 the regular, linear arrangement of north and south tributaries as is shown 

 on the Spanish maps or the later American editions based on them. 



Terraces along this river are well shown, following the south fork below 

 Tamontaca and on the north branch back of Ungup, and again near the 

 confluence of the Libugan and the Bio Grande. Between the town of 

 Cotabato and old Fort Tamontaca there is an extensive, raised, flat- 

 topped platform which rises like an island in the delta. This was 

 examined and found to be a raised coral reef 5 to 10 meters above the 

 level of the river. 



The Bio Grande, or Pulangi, overflows its banks periodically and thus 

 irrigates and enriches an already marvelously fertile soil. Bice is the 

 chief crop produced, but the methods of agriculture are very primitive. 



5 Also termed the Pulangui and the Cotabato. 



