652 RECORDS. 



Rhode Island Mine. The sides of the cavities in the coarse 

 conglomerate are encrusted with similar salmon-colored to red 

 grains and crystals, usually less than 0.5 mm. across, but var^^- 

 ing up to 3 mm. Coarse pebbles also occur here, up to 3 cm. 

 across, which seem to be made up of the same feldspar in dull 

 red grains. 



Schoolcraft Mine. The amygdules in the trap (brown amygda- 

 loid) are lined by copper, forming the outer shell ; inner layer, 

 red feldspar with interior filling of calcite or delessite. 



Orthoclase crystals have also been noted in the conglomerate 

 or amygdaloid, by H. Bauerman, R. Pumpelly and others, at 

 the Phenix, Bohemian, Amygdaloid, Bay State, St. Mary^'s, 

 Southside, Evergreen Bluff, Michigan, Sheldon and Columbian, 

 Ossipee, and other mines of this district. 



In the Ontonagon region, the cavities of the coarse conglom- 

 erate contain scattered crystals of the same red feldspar, 2 to 3 

 mm. across. Many pebbles of quartz-poiphyiy also occur, 

 whose small phenocrysts seem to consist of the same form of 

 orthoclase. 



All the observations point to a wide distribution of this variety 

 of the mineral throughout the copper-bearing rocks of the Lake 

 Superior region, in the cavities of the conglomerate and of the 

 cellular traps. 



Form. — The crystals are invariably of a simple type, in most 

 cases rhombic prisms. In the drusy cavities of the amygdaloid 

 at the Calumet Mine, to which the following description applies, 

 the crystals display a single modification, an orthodome on the 

 opposite obtuse angles. Skeleton forms are also common, made 

 up of thin plates, sometimes bent, parallel, or arranged in empt}' 

 box-like outlines, following rhombic contours ; these are plainly 

 results of under-development from lack of material. But else- 

 where, in the cavities of the amygdaloid, some feldspar surfaces 

 present a corroded or eaten-out appearance, with dulled lustre, 

 perhaps affected by the same solvent which has carried awa}' the 

 calcite from the core of these geodes. 



Many faces and cleavage-planes also exhibit distinct curvature 

 which in some cases is due to man\- successive offsets of laminfe 



