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PROCEEDINGS OP THE AMERICAN ACADEMY 



itself to the surfaces of the freely crystallized faces of the epidote 

 crystals; 5th. aniygdules filled with epidote alone in crystalline masses 

 radiating from several circumferential points into the interior. 



In thin sections of the matrix, the plagioclase crystals retain, in many 

 instances, tolerably defined twin striation in polarized light ; but nearly 

 all of them are partially, others wholly, changed to chlorite, which 

 forms connected pseudo-amygdules throughout the matrix. Numerous 

 characteristic pseudomorphs, with specular iron, after chrysolite occur. 

 But with the exception of some characteristic pseudomorphs, all the 

 pyroxene is now represented by calcite pseudomorphs, each showing 

 integral polarization. Some of the plagioclase crystals seem, also, 

 partly altered to calcite with aggregate polarization. The change 

 from pyroxene to calcite was apparently here, as in the melaphyre out 

 of Mabb's vein, the last transformation. 



If we consider the prehuite to be the oldest member of the arayg- 

 dules, as we have heretofore found it to be, and assign its age to the 

 period of formation of the pseudo-amygdules out of the plagioclase, 

 we shall be justified in considering the chlorite and quartz amygdules 

 as produced before the formation of the calcite pseudomorphs after 

 pyroxene. For we have seen the change of prehnite amygdules to 

 chlorite and quartz, where the pyroxene of the matrix was almost 

 intact. The pseudomorphs of epidote after prehnite were probably 

 mediated by the infiltration of the dissolved products of alteration of 

 the pyroxene. 



If this interpretation be right, the paragenetic tree should be : — 



/' — 



MA TRIX. 



AMYGDULES. 



A 



1. Chrysolite. 2. Plagioclase. 



3. Pyroxene. 



(II.) Characteristic 

 pseudomorplis with 

 specular Irou. 



(III.) 

 (IV.) 



(V.) 



(VI.) 

 (VII.) 



Chlorite pseu<lomorph8 

 and pseudo-amygdules. 



Characteristic 

 pseudomorphs. 



Prehnite from 

 plagioclase of matrix. 



1. Chlohite and 

 Quartz. 



Epidote. 



Calcite partial 

 pseudomorphs. 



Calcite 

 pseudomorphs. 



Calcite. 



