﻿ASBESTOS AND MANGANESE DEPOSITS. 153 



THE BOJEADOR ANDESITE. 



The main road from Pasiiquin to ISTagpartian follows the coast and just 

 a little past Bojeador light-house it cuts through a spur of the same hill 

 on which the light-house stands. At this cutting the rock which is 

 exposed is a light-colored andesite, very like some phases occurring at 

 Marivcles. This flow seems to constitute the main part of the rock mass 

 of Cape Bojeador. I regret that time was not available for a close study 

 of the field relations of this flow; it doubtless has some very close con- 

 nection in point of time with the "eruptive conglomerate." Many of 

 the bowlders and fragments in the latter mass are petrographieally quite 

 similar -to this flow. I found no other signs of this andesite flow any- 

 where else in the district. This flow, in all probability, is to be correlated 

 with the great andesite sheet of Benguet, described by Mr. A. J. Eveland, 5 

 formerly geologist of this Bureau, with a similar flow in Marinduque, 

 and with that of Cebu. 11 In the latter island it is found unconformable 

 above the upturned and truncated coal measures and below the orbitoidal 

 limestone capping. I shall not here enter into a detailed description, 

 as farther below I describe sections of practically identical rocks from 

 the "eruptive conglomerate." 



"eruptive conglomerate." 



A long, narrow, black and exceedingly forbidding ridge begins near 

 Cape Bojeador and extends due east therefrom for several miles at an 

 elevation of 1,500 feet; it is composed of masses of lava bowlders, some 

 rounded, more of them angular and fragmentary, all in a very mixed 

 condition and in a matrix which is also of volcanic origin. For purposes 

 of convenience, and from its analogy to a similar formation in Borneo 

 described by Verbeek, 7 I have called this an eruptive conglomerate; it is, 

 more strictly speaking-, an agglomerate. 



A line of much lower hills also exists, extending eastward between the 

 main road and the coast as far as Baruyen Biver; these hills are of the 

 same material. The manganese oxide which will be discussed in sub- 

 sequent pages occurs in the minute veins between the harder fragments 

 in the decomposed matrix. 



Plate V, fig. 5, is a view taken from one portion of this ridge, looking 

 down on the low country near the coast. Some trails in the uncut jungle 

 are more difficult, but apart from these, this one across this ridge is the 

 roughest one which it has been my lot to travel in the Philippines. I 



5 Eveland, A. J.: Geology and geography of the Bagnio Mineral District, to 

 lie published in the next number of Uiis Journal. 



"Smith, W. D. : Physiography of Cebu Island, this Journal (1000), 1, 1044. 



7 Verbeek. R. D. M. : Die Eociinformation von Borneo, nnd ihre Verstein- 

 emngen, Cassel (1875), 7. 



