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University of California. 



[Vol. 2. 



seems to occupy the entire southern part of the Peninsula of 

 Azuero, forming important mountain masses in the interior and 

 exceedingly ragged cliffs on the coast. It is beautifully exposed 

 on the shore of the Pacific Ocean on the west side of the peninsula, 

 both north and south from the mouth of the Torio River. Here it 

 is a massive fine-grained crystalline of very basic composition and 

 a characteristic green color. Unfortunately, my petrographical 

 knowledge was very crude at that time and no fragment of this 

 rock was brought away. Because of its general resemblance to a 

 Jurassic diabase in northern California, I discriminated it as a 

 diabase, but I am now more inclined to believe that it is a peridotite, 

 although nowhere prominently serpentinized. One of the principal 

 constituents is a semi-vitreous, transparent mineral of a greenish 

 gray color which may be olivine. 



An important part of the eruptive mass is an equally fine- 

 grained but dark brown and black rock, which under a hand micro- 

 scope was seen to be composed of black crystals of hornblende 

 and a lesser quantity of light brown feldspars, and hence resembling 

 a diorite. This appears to be in the form of huge dikes cutting the 

 green rock. The whole formation is streaked by many exceedingly 

 irregular veinlets of white quartz and calcite. Some veins contain 

 a red mineral of the color of cinnabar, but the staining matter is 

 probably iron oxide. 



Up the Torio River, the green rock sometimes assumes a 

 schistose character, sometimes that of a non-laminated slaty rock, 

 and again is clearly an eruptive. It is possible that the complex 

 may include highly metamorphic sedimentaries. Everywhere it is 

 characterized by the veinlets of quartz. 



By far the most peculiar thing connected with this formation is 

 certain large irregular masses of structureless, hard, bright red 

 quartz which are of frequent occurrence in the green rock near its 

 contact with later formations, and in the interior of the peninsula 

 has weathered out and lies in great boulders in the bed of the 

 Torio River. Some of these masses contain hundreds of cubic feet 

 and others seem to occupy ancient fissures several feet wide. The 

 only thing closely resembling this quartz or chert that I have ever 

 observed is heavy-bedded portions of the radiolarian cherts of the 



