338 The Philippine Journal of Science 1915 



ing closely with the increase in vegetation. Analyses, however, 

 proved the iron content to be just as high in the earth which 

 supported the heavy forest as in the more highly colored mantle 

 on the bare hills. 



Specimens of a half dozen of the plants which are most abun- 

 dant over the barren portions of the ore deposit were submitted 

 to Mr. E. D. Merrill, botanist of the Bureau of Science, who stated 

 that they belong without exception to the flora of high al- 

 titudes in the Philippines.^ The best-known types had not 

 previously been found below an elevation of from 500 to 600 

 meters and were commoner at elevations of 1,500 meters, where- 

 as the specimens submitted were all secured at elevations rang- 

 ing from sea level up to possibly 200 meters. Two of the 

 specimens were evergreens belonging to the pine family, another 

 was an edible blueberry which is common in the highlands of 

 northern Luzon, while the commonest plant observed is the 

 weedlike fern already mentioned. Pitcher plants, some of 

 which produce pitchers of extraordinary size, abound in the 

 region of the iron-ore deposit, but these, also, are found in other 

 parts of Surigao. 



GEOLOGY 



The iron ores are clayey residual products from the surface 

 decomposition of igneous rocks. They are similar to the later- 

 ites in origin found commonly in tropical countries. The 

 parent rock in Surigao is subsiliceous in character and is prob- 

 ably a peridotite, but wherever exposed it is so completely altered 

 as to make the determination of its original character difficult. 

 The outcrops which are most widely distributed consist essen- 

 tially of serpentine. On the beach, throughout the length of 

 the deposit, rocks of other types are found locally and probably 

 occur as dikes cutting the main rock mass. The dike rocks 

 include diorites, gabbros, and felsitic to porphyritic andesites. 

 Schist has also developed locally, probably in shear zones, and 

 occurs in rare fragments along the beach. 



Sedimentary rocks, principally tuff-sandstone and crystalline 

 limestone, overlie the igneous basement, the alteration of which 

 has given rise to the iron ore, and the line of contact between 

 the basement rocks and the overlapping sedimentaries marks 

 the limit of the ore deposit toward the interior. The sedimen- 

 taries outcrop on the coast at Capandan southeast of Claver 



' Unfortunately Mr. Merrill's memorandum containing the classification 

 of these plants was misplaced and because of his absence on leave cannot 

 be replaced in time for publication in this paper. 



