296 



PROCEEDINGS OP THE AMERICAN ACADEMY 



with epidote. These appear to have formed at the cost of the plagio- 

 clase. Some of the plagioclase crystals, especially near these pseudo- 

 amygdules, are partially changed to aggregates of epidote. 

 Paragenesis : — 



MATRIX. AMYGDULES. 



(I) 



(II.) 

 (HI.) 



(^^) 



(V.) 

 (VI.) 



1. Chrysolite. 



Characteristic 

 pseudoniorphs. 



2. Plagioclase. 



3. Pyroxene. 



Cliaractoristic 

 pseudomorphs. 



Prehnite forming 

 pseudo-amygdulos. 



Orthoclase 

 pseudomorph. after prehnite. 



Pkkhnite. 



Orthoclase 

 pseudomorph. after prehnite. 



1. Epidote and 2 Quartz 

 pseudoiuorphous after ortlioclase. 



' Spike Amygdules. — I have before me a specimen from one of the 

 mines working in an amygdaloid. It has an even purple-brown matrix, 

 in which occur isolated porpliyritic crystals of red feldspar sometimes 

 .j^ inch in size. Some of these may be orthoclase, as they show no 

 twin striation on the cleavage planes in reflected light, while others 

 are evidently triclinic. The loupe discovers numerous minute flakes of 

 specular iron. Besides these, there are many very small round amyg- 

 dules of chlorite, each forming a sphere with radiating structure, while 

 others, always larger ones, have an outer ring of this chlorite, and a 

 central filling of calcite, in which the uninterrupted cleavage indicates 

 a single individual. The rock contained, also, many irregularly cylin- 

 drical cavities, often 5 inches long, and -j'^ to ^ inch thick, running 

 parallel to each other and perpendicular to the plane of bedding. 

 These are now filled chiefly with metallic copper, in continuous, more 

 or less solid masses, which break out from the rock in the form of 

 rough-sided spikes. Many of the small, lound cavities adjoining a long 

 one are connected with it and filled with copper, so that, when the 

 large spike is detached, its sides have numerous small copper amygdules 

 joined to it by a neck. 



Besides the copper, these cavities contain quartz, calcite, and chlorite. 

 The chlorite forms the oldest member, lining the walls of the former 

 cavity ; quartz, more or less massive, with frequent perfect prisms, 

 comes next. Younger than the quartz ai-e copper and calcite. The 

 large calcite individuals break out with perfect casts of the quartz 



