368 SMITH. 



basalt. I have made no detailed study of the corals in these exposures, 

 but they appear to be identical in species, certainly in genera, with those 

 living in the sea immediately below. 



The fall of the Agus is a magnificent spectacle. The water from the 

 river drops 58.3 meters over a cliii of basalt to the gorge below. The 

 principal part of the formation is a hard, olivine basalt with a tendency 

 to columnar jointing. In the vesicular spaces there are white to greenish- 

 yellow minerals with radial structure, some ra3^s being over a centimeter 

 in length. This mineral is usually one of the zeolites. Calcite is found 

 in some of the specimens. 



Tbe formation changes rather sharply to an agglomerate in which 

 are numerous boulders about half-way down the side of the gorge. 

 The lower part of the formation is very porous and water can be noted 

 issuing in little streams from many points in the side of the cliff. 



Under the microscope the rock is seen to consist of the following principal 

 minerals: labradorite feldspar, rhombic pyroxene, olivine, and magnetite. Some 

 of the plagioelases are more than 5 millimeters in length. The pyroxenes are 

 alinost as large. The groimd-mass consists of an ophitic mat of well defined, lath- 

 shaped plagioelases, among which are scattered roundish grains of pyroxene, 

 olivine, and magnetite. The rock at Mataling Falls south of Lake Lanao is of 

 very much the same character. 



I have already stated that 1 found one outcrop of sandstone near 

 the Malaig Eiver, which drains Lake Budig ^nd flows into Lake Lanao. 

 This sandstone was very much weathered and very closely resembled 

 those overlying the coal in Cebu. It is not at all improbable that 

 drilling- at this point would reveal the coal measures below the level 

 of the lake. 



I made a trip in 1906 from Iligan into the hills southeast for a 

 distance of about fifteen kilometers. Here I found andesitic agglom- 

 erate, and in the beds of the streams I picked up many pebbles of schist 

 which must have been brought down from the hills on the boundary 

 line between Lanao and Bukidnon. About two kilometers from Iligan 

 I saw a little residual limestone from which I procured the fossil Turbo 

 borneensis Bttg. 



The traveller, after leaving Mataling Falls, very soon passes into an 

 extensive deposit of bluish-gray volcanic ash. This continues to Mala- 

 bang on the coast. 



- Putting all of these facts together, I believe that the stratigraphy 

 of Lanao is much the same as that of the Zamboanga district. At the 

 base we have diorite as witnessed by the diorite pebbles in the Iligan 

 Eiver; above this is sericite and chlorite schist, then sandstone, and 

 probably the whole coal measure series, which, however, may prove to 

 be contemporaneous with the schists; and finally, piedmont deposits 

 around the border of Lake Lanao. and those along the lower reaches 

 of the river. 



