OP ARTS AND SCIENCES. 



307 



loids or middle zone, and which the more highly altered forms of the 

 amygdaloids proper : — 



Plagioclase and Matrix. 



Prehnite. 



Pseudo- 

 amygdaloidal 

 chlorite. 

 ( Very com- 

 mon.) 



Soft yel- 

 low-green 

 substance. 



Clay 



and 



chlorite. 



Orthoclase. Orthoclase. 

 (.SedW.) (50 /i IF. 

 of 

 Hough- 

 ton con- 

 glomerate. 



Epidote. 



Calcite. 



(■s 



Chlorite. 



Soft yel- 

 low-green 

 substance. 



Chlorite. 



Orthoclase. 



Epidote. Epidote. Epidote. 



Green- 

 earth. 



Calcite. 



Quartz. Quartz. Quartz. 



{Bed 69.) {Sec. 8, 

 T. 47, 

 a. 45.) 



Quartz, 

 replacing 

 calcite. 

 {Huron 

 Jiline.) 



Quartz. 



Copper. 



{SpUce 



amygdules.) 



"With few exceptions, the course has been as follows : — 



Pseudo-amygdaloid 

 stage. 



Amygdaloids. 



I. Hydration of chrysolite, when present. 



II. Change of augite, loss of lime, and partial loss of 



iron and magnesia. 



III. Change of feldspar to prehnite, and formation of 



prehnite psendo-amygdules. 



IV. Change of prehnite to chlorite. 

 IV a. Cliange of prehnite to orthoclase. 



I. Filling amygdaloidal cavities with prehnite, or other 

 minerals. Change of matrix to ferruginous preh- 

 nite. 

 II. Change of the prehnite, in places, to chlorite; in 

 others, to calcite and green-earth; in others, to 

 epidote and calcite. 



III. Entrance of quartz, filling all the interstices and 



replacing the calcite. 



