70 ADAMS. 



within. A close examination of the direction of dip of the lava beds would give 

 definite conclusions in regard to this." 



To the west of Corregidor there is the small volcanic island La Monja and to 

 the south the rock El Fraile. These also show clearly that they are formed of 

 lava." 



Becker refers to the statements of "Von Drasche which suggest that 

 Corregidor and Caballo Islands are parts of the rim of a large crater and 

 says that this also appeared probable to him during his visit to these 

 islands. 



The only record of an actual examination of any part of Corregidor 

 appears in the writings of Becker, who says : "I found an interesting 

 dacite on the Island of Corregidor, at the entrance to Manila Bay. It 

 forms a wide irregular dike crossing the island, from north to south 

 just east of the little settlement of San Jose, and terminates in a bold 

 white cliff visible from the south passage or Boca Grande." He described 

 in detail the appearance and microscopic structure of the rock. 



This is the only exposure of igneous rock which was seen on the island. 

 Becker says the dacite is a dike but he does not state what rocks it cuts. 

 With the exception of the bluff on the south side of the island it is 

 surrounded and partially overlaid by marine conglomerates with a 

 variable matrix which grades into thick beds of finer sediments. The 

 conglomerate is exposed in vertical bluffs around the western part of 

 the island and on the eastern part it is weathered and shows stratification 

 and slight folding and some faulting. On the main part of the island 

 the conglomerate was seen well exposed in the excavations made for 

 fortifications up to an altitude of about 150 meters. The highest point 

 of the island is about 200 meters above the sea. There are no good 

 exposures on this dome-shaped portion, but there are numerous bowlders 

 lying on the surface and imbedded in the surface cla}'. These are 

 andesites and it is probable that there is a mass of andesitic rock which 

 forms the core of the higher, western part of the island and the bowlders 

 in the conglomerate have been derived from it. There are no lava beds 

 on the island, but the matrix of the conglomerate and the beds of finer 

 sediments contain tuff and volcanic ash evidently from distant sources. 

 The eastern part, or tail of the island, as it is called, has an average 

 elevation of about 75 meters and in so far as seen consists of conglomerate 

 beds. The present position of the marine conglomerates indicates an 

 elevation of Corregidor Island of about 200 meters. They are the 

 equivalent of those found on the mainland near Sisiman and Mariveles. 



Exposures of conglomerate were seen up to an elevation of 100 meters 

 at Olongapo on the ridge to the north of the CalaeanBiver and to the 

 east of the rifle range, and there is a bluff of conglomerate facing the 

 lowland northeast of Subig. 



By far the most important area of this formation is to be found on 

 the north and west flanks of the Pico de Loro Mountains to the south of 



