OF ARTS AND SCIENCES. 295 



(I.) 1. Chrysolite. 2. Plagioclase. 3. Pyroxene. 



I (AnortUite.) 



(II.) Characteristic 



pseudoniorphs with 

 specular iron. 



(III.) 



(IV.) 



Prehnite. 



Few of the characteristic 

 pseuJomorplis. 



(V.) 



1. CLAY-like product. 2. Chlorite. 2 a. Orthoclasb. 



One hundred and jifty-eight feet west of the Isle Eoyale copper-hearing 

 bed, on the Sheldon and Columbian property, there is a very interest- 

 ing amygdaloid. It has an aphanitic, brownisli-green matrix, abound- 

 ing in amygdules of rather irregular shape, but with sharply defined 

 contours. These vary from microscopic size to several inches, the 

 larger ones having the most irregular forms. The larger ones consist 

 of intimately associated white prehnite, granular red orthoclase, quartz 

 and epidote. The smaller ones, containing little prehnite visible with 

 the naked eye, have an outer member of red orthoclase freely crystal- 

 lized in the middle, and have in the centre, quartz, or epidote in small 

 crystals, or boih. 



The feldspar crystals are profoundly altered, and present now mere 

 honeycombed forms. 



In thin sections, the orthoclase pseudomorphs after prehnite still 

 polarize the light ; but such of the feldspar substance as remains is 

 rendered impellucid by many suspended particles of iron oxide ; and 

 the honeycomb cells are filled with quartz, which also occupies the 

 central area of the amygdule. Epidote, in short and long prisms, occurs 

 within the feldspar foi-ms, and often starting in the cavernous interior 

 projects beyond the end of a feldspar, and is there wholly enclosed 

 in quartz ; it also occurs apparently wholly suspended within quartz 

 individuals. 



In the matrix, relatively few of the plagioclase crystals show a just 

 apparent twin-striation in polarized light. In most of them it has dis- 

 appeared. There is no unaltered pyroxene, but there are some of the 

 characteristic pseudomorphs after that mineral, and others after chryso- 

 lite. The interstitial spaces are filled with an iron-stained, soft, slightly 

 green substance, somewhat resembling that of the pseudo-amygdules. 

 .Besides this, the matrix is in many places filled with pseudo-amygdules, 

 — many wholly occupied by epidote aggregates, others by orthoclase 



