xii, a. 6 Hcise: Radioactivity of Waters, Northern Luzon 303 



is generally more radioactive than that from sedimentary 

 deposits."' 



The geology of the area discussed in this report has unfortun- 

 ately not been worked out in sufficient detail to justify generaliza- 

 tions; hence it is not feasible at this time to attempt to deduce 

 any definite relations between radioactivity and the geology of 

 the water-bearing strata. The following description by Smith n 

 of a typical portion of this region is appended for the sake of 

 completeness : 



This region is typically mountainous, and from the character of the relief 

 we must consider it as being in the stage of "topographic youth." * * * 



There are two distinct types of topography in the region covered by 

 this paper, and these are directly to be attributed to the character of the 

 geologic formations. In the country to the west of the Polis Range the 

 formations are mainly volcanic, and we find there an irregular, rugged, 

 accentuated relief. The elevations vary from 370 meters to 2,400 meters 

 or more. 



East of this range the formations are folded sediments, giving rise to 

 a more regular topography, and in places the hills and mountains are 

 nothing more than tilted blocks of sandstone. On the eastern slopes these 

 present long, gentle inclines, but to the west they form steep escarpments 

 with here and there a saw toothed skyline. As one goes farther to the 

 east, approaching the valley of the Cagayan, the mountains become mere 

 foothills. * * * 



A cross section from the west coast at Tagudin northeastward to the 

 edge of Cagayan Valley gives as good a general idea of the formations and 

 structure of the region as one could expect to get by any procedure short 

 of a detailed survey of the whole country. Fig. 2 is a graphic attempt to 

 record my interpretation of the main facts. 



Near the west coast we find gently folded shales and sandstone whose 

 inclination increases as we go toward the Malaya Range, being much 

 contorted as we get well into the canon. The Malaya Range is essentially 

 a mass of porphyry or, to be more exact, andesite. * * * 



The town of Cervantes is situated on a small tongue of high ground 

 between the Abra and one of its branches. The underlying rocks are 

 practically the same as those found in the highland on both sides of the 

 town. As we go toward Bontoc we find the same andesitic mass with, 

 however, several large outcroppings of quartz. 



When we reach Bagnan and Sagada we find tuffs and reef limestones 

 overlying this igneous mass 



"From Sagada to Bontoc extrusive rocks, almost entirely andesites and 

 dacites, are encountered but east of Bontoc the formations become very 

 shortly diorite and granite. This belt of granitic rocks is only from 8 to 

 10 kilometers wide. There is more andesite, or rather a very fine-grained, 



10 One of the most radioactive waters in the lowlands, from Sibul Springs, 

 Bulacan, is also in a calcareous formation, and others high in activity issue 

 from tuffs and conglomerated igneous materials. 



u Smith, W. D., Notes on a geologic reconnaissance of Mountain Province, 

 Luzon, P. I., This Journal, Sec. A (1915), 10, 177-209. 



