ISO "^he Philippine Journal of Science ms 



appears to have an east and west extension. In this ore body the ore 

 occurs in veins that likewise follow an east-west direction, so that all pal- 

 leries having a north-south direction expose all the seams. These veins at 

 places are supposed to be 7 meters in width and are uniformly steeply in- 

 clined. The distance between these very regular veins, in general, is very 

 little. The ore minerals are principally luzonite, enargite, and covellite, 

 the first-named occurring abundantly in beautiful crystals; besides, I 

 noticed baryte, calcite, copper sulphide, malachite, copper sulphate 

 stalactites, arsenic, and a saponitartiges mineral stained blue by copper 

 salts. 



Limestone is used in smelting the ores, which is quarried at Mount Ma- 

 laya, in the cordillera west of Mancayan; judging from the pieces which 

 I saw, it is a coralline limestone. Much gold is said to be panned [washed] 

 south of Mancayan in the mountains of Suyoc and Tubuc, and I was in- 

 formed also of the occurrence there of hills of gypsum containing cry.stals 

 of iron-pyrites. According to this information it appears that a part of 

 that extraordinarily serrated mountain chain, which, according to Peiia- 

 rubio's map continues in the shape of an arch from Suyoc to Pico Tila and 

 then turns directly north, consists of coralline limestone. The northern 

 continuation is, as we shall see, formed almost entirely of this stone. 



I continued my journey from Mancayan to Cayan, the capital of the 

 district of Lepanto. One descends the heights, consisting of sanidine- 

 hornblende-trachyte, and very soon reaches again a narrow belt of the 

 Agno beds. Before crossing over to the left bank of Abra River, one 

 encounters large bowlders of an excellent rhyolitic quartz-trachyte. It is 

 noteworthy because of its beautiful flow structure. It is possible to dif- 

 ferentiate a quartz-trachyte with a dark gray groundmass and another 

 variety with a red groundmass. Both coalesce in varied Schlieren, as 

 Dr. Reyer would say. 



In this dense, hard, splintery groundmass there are found closely packed, 

 numberless water-white splinters of quartz. These are never rounded, 

 nor do they show the least trace of regular structure, but are always charac- 

 terized by their fragmental nature; at times they attain a diameter of 

 4 millimeters. It is interesting to note that the gray Schlieren only contain 

 nests of pyrite. Thin sections of the rock give no information whatsoever 

 concerning the nature of the groundmass. It is very apparent to the eye 

 that the quartz fragments were not formed out of the groundmass; on the 

 contrary, it is apparent that they were enveloped by the magma which 

 formed the groundmass. I regret that I did not succeed in discovering 

 this interesting trachyte, which certainly has an extraordinarily high silicic 

 acid content, in place, although very large blocks of it are found in the 

 river bed of the Abra. As was indicated on page 36 the copper lodes of 

 Mancayan are found to occur in a quartz lens. There are also found with 

 the quartz-trachyte bowlders a great many fragments of a crystalline 

 quartz, which are stained red in places and marked along fracture planes 

 with iron. It might be appropriate to give an explanation of the origin 

 of this remai-kable trachj'te. 



If a dike of the rhyolite broke through one of the quartz lenses, it is very 

 possible that on its borders there would be formed similar breccialike rocks. 



The banks of the Abra are composed of an exceedingly coarse, dolerite 

 breccia; the fragments, somewhat rounded and about the size of a clenched 



