486 



ICKIS. 



At the mouth of the Maeailata I?iver a dark rock was ob.served, with a 

 slight greenish tinge containing light colored phenocn'Sts and amygdules 

 of white stilbite. Under the microscope the ground mafs is seen to be 

 typically andesitic but the felds))ar plionocrysts can not be identified. 



Near the mouth of the Calua a tough, hard, dark colored rock was 

 foiind in i^laces, which has tlie appearance of a basalt and sliows many 

 red spots, proljably oxidized iron of the ferromagnesium minerals. A 

 few crystals of striated feldspar are visible in this rock. By microscopic 

 examination it was determined to be of a tuff consisting of consolidated 

 fragments of andesite as well as of some large individual crystals of 

 hornblende. Feldspars in some of the rock fragments show almost com- 

 plete alteration. 



The river valley below the Ma-cadata is 200 to 600 meters wide. On 

 both sides, the hills are marked by high sharp ridges and deep narrow 

 gullies, and are covered with a hea^7 forest growth. There are some 

 sharp bends, but there would be no unusual difficulties to overcome in 

 constructing either a wagon road or railway along the river banks. 



Sedimentaries, consisting of limestone and shale in various stages of 

 metamoi-phism, appear a short distance above the llacadata and continue 

 as far as the ridge north of Tanay which forms part of the main divide 

 of Luzon. A hot spring bubbles up in the river near the contact between 

 the igneous and sedimentaries above the Macadata, from which the 

 locality has received the name Mainit (hot spring). The first sedi- 

 mentaries are shale beds striking IST. 30° W. and having a dip of 80° W. ; 

 these are followed by vertical beds strilcing IST. 10° E. The guides here 

 left the river, taking the party over a heavily wooded ridge and down to 

 the river again where the rock is bedded limestone having a strike of 

 N. 10° W. and a dip of. 60° toward the east; a kilometer \ip the stream 

 the dip of the beds is reversed to 45° to the west, the strike remaining 

 the same. This rock was determined microscopically by Doctor Smith 

 to be foraminiferal limestone containing Orbitoides. Lrpidoryclifia in- 

 sidac-nataJis, Jones and Chapman. The rock is from light gray to cream 

 color, hard and compact. Fossils are most numerous in the gray rock 

 but are not distinguished in either without careful examination. A 

 pebble picked up near the mouth of the Agos was found to be forami- 

 niferal limestone containing Cycloclypeus, a common miocene fossil. 



The river bed is narrow and the walls precipitous through this lime- 

 stone belt which is about half a mile in width. To the westward, shale 

 beds and graywacke appear again, and an open and com])arativelv level 

 country, tlie source of the Agos Eiver, is seen to the northwest. One 

 sample collected and classed as a graywacke is seen under the microscope 

 t.o be composed of grains of silicates, some of which are roimded, others 

 not, biit all are clastic and consist mostly of fragments of plagioelase 

 felrfspar; megascopic examination showed a greenisli gray rock some- 

 what gritty to the touch. Some fractures have a irreasv luster. 



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