PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 439 



Wood. Calcite and Galenite. 

 Graphite. Diabase.] 



No. 586. WOOD. 



Minong mine, Isle Royale. 



Ref. Annual Report, x, page 54. 



Found in the ancient mines. For an account of these ancient miners, by N. H. 

 Winchell, the reader may consult the Popular Science Monthly, September, 1881. 



N. H. W. 



No. 587. CALCITE AND GALENITE. 



Silver Islet. 



Ref. Annual Report, x, page 55. 



Meg. A mass of crystals of calcite and galenite, with a very little pyrite. The 

 crystals of galenite show combinations of the cube and octahedron, the latter usually 

 being better developed. 



Age. Vein in Animikie rocks. u. s. G. 



No. 588. GALENITE. 



Silver Islet. 



Ref. Annual Report, x, page 55. 



Mey. A mass of octahedra of galenite. .The largest of these crystals is over two 

 inches across. 



Age. Vein in Animikie rocks. u. s. G. 



No. 589. GRAPHITE. 



Silver Islet, 



Ref. Annual Report, x, page 55. 



Meg. The hand sample is apparently a mass of much decayed rock which has 

 been impregnated and partly replaced by graphite. The original nature of the rock 

 is not clear; it now contains a little calcite. The hand sample resembles somewhat 

 the graphitic quartzyte from Pigeon point (No. 270). Probably a third, or possibly 

 half, of the rock is graphite. 



No section. 



Age. In a vein in the Animikie. This is from the great vein at Silver Islet. 



u. s. G. 

 No. 590. DIABASE. 



Silver Islet, Thunder bay. Prom the great dike at the bottom of the mine, 720 feet below the level of 

 lake Superior.* 



Ref. Annual Report, x, page 55; Bulletin ii, page 116. 



Meg. A medium-grained, gray, massive rock, crossed by several thin veins of 

 calcite. 



Mic. The minerals are all considerably changed, notwithstanding the great 

 depth from which the specimen was obtained, a circumstance which may be attrib- 



*For an account of the discovery and working of the silver deposits of Silver IsM, the reader may consult MACFARLANE, 

 Transactions of the American Institute of Jfintnii r.n </iui : crs, viii, p. 236. 



