PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 441- 



Breccia. Diabase. Slate.] 



No. 592. BRECCIA (of slate). 







Silver Islet. From the vein of the Silver Islet mine. 

 Ref. Annual Report, x, page 55. 



Meg. Angular fragments of slate are cemented by the gangue rock No. 591. 



Mic. A section of the marble shows a confused massive growth of calcite, with 

 a small amount of quartz, and a single grain that appears to be tifanite, resembling 

 the titanite of No 590. 



One section. 



Age. Vein in the Animikie. N. H. w. 



No. 593. DIABASE. 



From a breccia in the vein of the Silver Islet mine. 



Ref. Annual Report, x, page 55; Bulletin ii, pages 118, 120. 



This rock appears identical with No. 590, from the bottom of the shaft. 



Mic. There appears to be an element of leucoxene in the changed augites, giving, 

 along with a loss of polarizing power, a sub-transparency which is also specked with 

 opaque particles which are probably magnetite; otherwise the section is comparable 

 to that of No. 590. 



One section. 



Age. Vein 'in the Animikie. N. H. w. 



No. 594. SLATE. 



Silver Islet. The rock that encloses the vein. 

 Ref. Annual Report, x, page 55. 



Meg. Argillaceous slate, in which the laminae are due to the original sedimen- 

 tation. 



Mi/-. One thick section only affords the determination of a narrow vein of 

 granular quartz that crosses it. The rock is crowded with opaque substances. 



One section. 



Age. Animikie Taconic. N. H. w. 



No. 595. DIABASE (tu-ith hyfici-xt/ioie). 



Cores of the diamond drill at the bottom of the Silver Islet mine. 



Ref. Annual Report, x, page 55; Bulletin ii, pages 59, 92; Wadsworth, Bulletin ii, page 59. 



Meg. A diabase of medium grain, firm and gray. 



Mic. This rock is more nearly in its original condition than No. 590, but has 

 suffered some change similar to that seen in that rock. Quartz appears as a secondary 

 product both as micropegmatyte in the feldspars and as isolated grains between the 

 other minerals. Apatite is quite abundant piercing all the other minerals. The 

 feldspars are somewhat zoned and are twinned on the albite and pericline types. 



