GEOLOGICAL RECONNAISSANCE — INFANTA TO TANAY. 485 



sive Military Map of the Philippines, issued from the office of the chief 

 engineer officer, Philippines Division, United States Army, also ac- 

 curately represents the position and size of the Agos but does not indicate 

 the Canaan branch nor show the Alasasin correctly. 



My trip was made late in the dry season, but even at that time the 

 Agos Eiver below the entrance of the Canaan was found to be about 

 100 meters wide and from one-half to 1 meter deep at the rapids. The 

 Canaan enters the xlgos from the north at a point approximately 12 

 kilometers in a direct line from the mouth of the Agos. Although the 

 southern branch retains the name Agos above this point, the Canaan is 

 the larger stream and is entirely unexplored. This conjunction point is 

 called Pagsanjan by the Negritos, and the Agos Eiver abo-\e this point 

 is sometimes called the Calua, but usually simply the Agos. 



The main river' was left at a point about half-way between Infanta 

 and Tanay and a tributary called the Alasasin followed to within 7 or 8 

 miles of the latter j)lace. The Macadata, flowing in from the north, is 

 the only tributar^^ of any considerable size between the Canaan and the 

 Alasasin. 



Prom a low alluvial coastal plain at Infanta, not more than 3 miles 

 broad, a range of heavily wooded mountains rises rapidly to a height 

 of from 1,000 to 1,300 meters. This coast range is composed of andesitic 

 rock ranging from pure augite andesite to andesite porphyry, diorite 

 porphyry, and andesite tulf. The rock shows considerable variation in 

 structui'e but is apparently all andesitic as far west as the Macadata Eiver. 

 In the river bed a large variety of rocks is exhibited, including limestone 

 and hard siliceous shale as well as andesite and diorite bowlders. Some 

 of the andesite bowlders contain a large amount of secondary white 

 chalcedonic silica. The principal jointing planes in this igneous mass 

 appear to strike about N. 75° E. and dip 75° to the southeast. There 

 are also joints that strike nearly at right angles to these and dip steeply 

 to the northeast. 



A representative specimen from the eastern part of the coast range 

 consists of firm, tough, dark colored rock which, when unaltered, re- 

 sembles in outward appearance a basalt more than an andesite, the 

 phenociysts not being prominent; but when slightly weathered, the 

 plagioclase phenocrysts are conspicuous. Under the microscope it is 

 readily determined to be an augite andesite. 



A few hundred yards below the Macadata Eiver a fine-grained, dark 

 gray rock is present, the nature of which could not he determined mega- 

 scopically. Under the microscope the specimen is seen to be badly altered 

 as shown by magnetite in the midst of patches of red oxide of iron 

 and the uralitized pyroxene. The feldspars are all quite obscure ancl 

 clouded, belonging probably to an andesite porphyry. One specimen 

 of this rock contains white and green chalcedony. 



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