PHYSIOGRAPHY OF THE PHILIPPINE ISLANDS. 13 



waters near the pass, flows west by south into the Gulf of Asid. The 

 countrj between the ridge and the gulf shows even more clearly than on 

 the west that its lack of relief is due to combined erosion accompanied 

 by upbuilding from the wash from the ridge, rather than to uplift. In 

 other words, it is a plain of degradation rather than a true coastal plain. 

 Tlie loose material is largely composed of irregular gravel and there are 

 numerous small "monadnocks'' and outcrops of a red slate. 



The Gulf of Asid is a broad, shallow baj^ occupying the space between 

 the two prongs of the island. The deepest portion is along its western 

 shore, but it is nowhere over 40 meters in depth. At the head of the 

 bay, near Milagros, it deepens so gradually that there are 2 or 3 kilo- 

 meters of sand exposed at low" tide. The eastern side of the gulf is 

 very shallow and filled witli numerous reefs and small islands. The 

 barrio of Mangsalange is situated some kilometers to the east of Milagros, 

 whence the trail leads to the copper and lead deposits. Conditions here 

 are similar to those on the west shore of the gulf, but the plain is much 

 rougher because the hills are farther inland and lower and consequently 

 the surface is not smoothed by the piedmont wash deposits. A small 

 hill of hornblende andesite rises near the coast at Mangsalange and 

 further back is an irregailar jDlain with numerous small hills, capped by 

 a light-colored, coralline limestone. Outcrops of a red slate similar to 

 that found on the western shore of the g'l^lf, together with some jasper 

 occur in the stream beds. Farther inland the copper and lead deposits 

 are reached. jSTative copper occurs scattered irregularly through a mela- 

 pliyre, which is sheared and jointed along lines ru.nning north and jST. 

 60° E. Many veins occur nearby in a country rock of decomposed 

 feldspar porphyry, some of these carrying copper ores and others galena. 

 The usual strike is froin 10 to 20 degrees east of north, showing that 

 even as far east as this point the northeasterly series of lineaments is 

 still present. The white limestone found near the shore is no longer 

 present, but the small hills are capped with a dark limestone similar to 

 that found in the Guinobatan canyon in the Aroroy district. Thick 

 forest is encountered northward from this point towards Mobo, and 

 little can be seen of the general nature of the country. To all ap- 

 pearances a rather low, plateau-like ridge extends in a northwesterly 

 direction, with black limestone outcropping on its southern side and on 

 its summit, overlying a series of volcanic rocks, which in turn overlie the 

 older slates. 



Between Masl)ate and ililagros the ridge is broken by a broad, nortli- 

 easterljr trough, extending across the island, being a southwestward 

 prolongation of Port Palanoc. The dark limestone is also found in this 

 depression, showing that it is of comparatively early origin. 



Between Milagros and Lanang the country becomes more rugged and 

 the hills seem to be higher. This portion of the island is for the most 



