MINERAL RESOURCES OF AROROY DISTRICT. 413 



since on its northern border it seems to be cut off by an easterly vein. 

 However, this isolated occurrence of limestone must remain a puzzle 

 for the present. 



After the period of vein formation, submergence and the laying down 

 of the marine sediments occurred; these sediments are now found in 

 their early form in the extreme southern part of the area and in a later 

 phase on the opposite shores of Port Barrera. After the sedimentation 

 had gone on long enough to build up a very considerable mass of con- 

 glomerate, sandstone, and shale, a further change of level took place, 

 resulting in an unconformity which is marked by the conglomerate found 

 above the shale. The pebbles of vein quartz and andesite composing 

 this conglomerate show that the Panique formation and the veins were 

 then exposed to erosion and enable us to date the period of vein formation 

 with moderate certainty as between late Eocene and early Miocene. 

 Submergence again continued, giving the series of limestone terraces 

 that form such a prominent feature of the topography beween Point 

 Colorada and Point Bugui. It is to be inferred from the courses of the 

 present streams that the Aroroy district itself was at one time, at least 

 in great part, covered by sediments. ISTone of the principal streams 

 shows adjustment to the present topography, and all may properly be 

 classed as superimposed. After the period of sedimentation, the land 

 surface was elevated to a point probably some sixty meters above its 

 present level, and remained at this elevation long enough for a deep 

 valley to be eroded out of the soft shales. Eecent depression has converted 

 this valley into the present Port Barrera. Still more recent elevation, 

 but only to the extent of some five or six meters, is shown in the raised 

 coral reefs found on the northern shore of Point Colorada and on the 

 coast east of Buyuan Bay. 



ECONOMIC GEOLOGY. 



History of mining. — The veins of the Aroroy district have imdoubtedly 

 been worked since early times, even before the Spanish conquest. 



In the first and second volumes of Blair and Eobertson's monumental 

 work are ' short notices of the mines of Masbate in the reports of the 

 earliest Spanish explorers. An interesting description of the district 

 is given in the account by Gemelli Careri ^^ of his trip around the world. 

 His ship put in at a harbor on the Island of Masbate, evidently Port 

 Barrera, and he describes the mines as follows : 



They say Masbate is thirty Leagues in Compass, eight in Breadth and pro- 

 portionably Long. Its Ports are Commodious for any Ship to Water. In it 



-'A voyage around the world. By John Francis Gemelli Careri, 1695-1698. 

 Translated from the Italian. Published in A collection of Voyages and Travels. 

 Awnsham and Churchill. London (1704), 4, 436. 



