504 O. H. HERSHEY GEOLOGICAL RECONKAISSANCE IN KICAKAGUA 



gravel suggests an older volcanic series than that seen down the river. 

 A few pieces were doubtfully identified as diorite. 'No sedimentary rocks 

 were certainly represented^ certain shaly flinty rocks having been prob- 

 ably altered volcanic material. There were no typical rhyolites present, 

 though some of the pebbles appeared rather more acid than an andesite. 



The Pis-Pis River for about 10 miles upstream to the Yapooketan 

 Falls is in a trench usually 50 to 75 feet wide, which evidently winds 

 about in a floodplain. The banks are chiefly the brown sandy silt of the 

 Modern alluvium. At the falls the river probably cuts through a small 

 range of hills, as the banks are much higher and more uneven than far- 

 ther downstream. The river may fall 20 feet within 300 yards. To the 

 mouth of the Guavel Eiver the Pis-Pis is about 50 feet wide and flows 

 in a crooked trench largely lined with alluvium. Above the Guavel it is 

 reduced to a width of about 30 or 40 feet and has the usual alluvial 

 banks. The stream is a succession of long quiet reaches and short rapids. 

 The latter are so numerous that one is surprised to learn that the alti- 

 tude, as determined by aneroid readings, is but 472 feet at the Big Falls 

 bodega, the gateway to the Pis-Pis mining district. 



The topography of the Pis-Pis district is that of an ancient and deeply 

 eroded volcanic region. The more resistant rocks form the hills. The 

 principal valleys are generally eroded in andesite lavas and tuffs, but 

 where traversed by hard ribs of intrusive rock the streams cascade over 

 them in falls from 10 to 230 feet high. The district ranges in altitude 

 from about 600 to about 1,700 feet above sealevel, but much higher 

 mountains occur at a short distance on the northeast and northwest 

 sides. It is a curious fact that although it is on the divide between the 

 Wanks and Prinzapulca river systems, much more mountainous country 

 occurs in all directions from it except a small section on the north and 

 another on the southwest. There are several very low passes on the 

 divide. 



A view toward the south and west from near the Mars mine shows an 

 unsystematic grouping of many uneven-crested ridges covered by the 

 almost unbroken tropical forest. Some of them probably rise to 2,000 

 feet above sealevel. Their crests appear to be narrow and their slopes 

 generally steep. Between them are rather broad valleys, the floors of 

 which, however, are not to any great extent even. They are crossed by 

 low ridges of hard rocks, over which the streams cascade. Looking off 

 toward the north, there seem to be rather broad-floored valleys along the 

 main streams, as the Guavel, Pis-Pis, and Waspuc rivers, and the ridges 

 are low for perliaps 20 miles, but beyond that there are several prominent 

 mountain ranges apparently trending easterly. 



