OF AETS AND SCIENCES. 



297 



prisms, and the copper spikes are indented on the sides with impres- 

 sions of the quartz crystals, showing every detail, including the hor- 

 izontal striation of the prisms, with all the sharpness of an electrotype. 

 The relative ages of the copper and calcite does not appear. Both 

 the co25per and calcite form fine seams, traversing the matrix ; but they 

 were not observed together in the same crack ; and copper flakes abound 

 in the cleavage of the macroscopic feldspar crystals. 



On the sides of the spike-cavities, after removing the copper, were 

 found groups of very small, hard, green crystals, which seem to be 

 epidote. They are younger than the chlorite, and older than the copper ; 

 for this bears sharp impressions of the crystal groups. 



In thin sections of the matrix we find the isolated macroscopic 

 crystals of plagioclase, and more rarely others, which show no twin- 

 ning, and are perhaps orthoclase ; and these are undoubtedly primary 

 constituents. Aside from these, the matrix consists of small plagioclase 

 crystals, more or less altered, but generally showing the twinning in 

 polarized light, and lying in an almost continuously connected mass 

 of. pseudo-amygdaloid chlorite, which is frequently obscured by aggre- 

 gated flakes of specular iron and brown stains. 



Paragenesis : — 



MA mix. 



/•. 



AMYGDULES. 



(I-) 



(U.) 



1. Pl^AGIOCLASE. 



2. Pyroxene or Magnetite. 



Specu/.ae iron. 



(in.) Chlorite in connected 

 pseudo-amygdules. 



(IV.) 



1. Chlorite lining walls. 

 2 o. ? Epidote? 6. ? Quartz. 



(V.) 



3 c.? Copper, d. ? Calcite. 



A purple-brown amygdaloid from the Sheldon and Columbian prop- 

 erty has a very fine-grained matrix. It contains, 1st, sj^herical amyg- 

 dules, ^ to \ inch in size, of prehnite, more or less altered to a pliable, 

 white, chalky substance ; 2d, spherical amygdules, ^ inch and less, of 

 dark, green chlorite, with finely scaly texture, enclosing a little quartz ; 

 3d, spherical amygdules, with a central filling of the white altered 

 prehnite, of very irregular shape, and surrounded by epidote, with com- 

 paratively coarse crystallization, and seemingly pseudomorphous after 

 prehnite ; 4th, an amygdule of epidote, containing two irregular central 

 masses of calcite separated by a partition of epidote : the calcite adapts 



