1866.} BAUERMAN COPPER-MINES OF MICHIGAN. 459 



upon an epidote-breccia lode divided into two branches by a horse 

 or rib of barren trap. Yery extensive traces of aboriginal mining 

 have been discovered at this place, the old miners having sunk their 

 pits on both branches of the lode, avoiding the barren ground between 

 them. It is very remarkable that almost all the valuable mining 

 locations on the lake show traces of Indian or Aztec work; and 

 recent discovery has shown that they not only worked on the mass 

 lodes, but also — in one instance at least — on the conglomerates. If 

 the country were less wooded, these old workings might be of consi- 

 derable service in indicating the position of deposits of v-alue ; but 

 they are, in almost all instances, filled up and covered by vegetation, 

 the trees being as large as any of those of the surrounding forest, 

 thus giving proof of the remote antiquity of these workings. 



8. Paragenesis. — The following are a few of the chief alternations of 

 minerals observed in the Lake Superior mines : others will be found 

 in the works of Professor Whitney : — 



1. Chlorite, calcite, copper — Pewabic lode. 

 "2. Chlorite, quartz, copper — Isle Royale lode. 



3. Chalcedony, quartz, apophyllite, calcite — Bay State mine. 



4. Laumonite, quartz, green-earth — Phoenix mine. 



5. Prehnite, quartz, copper, laumonite — Bay State mine. 



6. Natrolite, laumonite, analcime — Copper Falls mine. 



7. Calcite, copper, analcime, orthoclase — Copper Falls mine, 



8. Apophyllite, copper, orthoclase — Copper Falls mine. 

 D. Datholite, copper, calcite — Copper Falls mine. 



10. AnaLeime, copper, orthoclase — Bohemian mine. 



11. Quartz, prehnite, copper, calcite, clay — Albany and Boston lode. 



12. Quartz, epidote, laumonite — Isle Royale lode. 



13. Quartz, epidote, copper, orthoclase, calcite, melaeonite — National mine. 



14. Calcite, prehnite, copper, cuprite, chalcotrichite, chryosocolla, allophane, 

 silver — Albany and Boston conglomerate. 



15. Calcite, chrysocolla, malachite, cuprite, silver — Albany Smd Boston conglo- 



merate. 



16. Quartz, Whitneyite — Shelden and Lexington mines. 



17. Copper-glance, calcite — Mendola min^. 



From the above list it will be seen that the copper is sometimes 

 older and sometimes newer than the associated minerals. In the 

 Ontonagon district it occurs very generally as incrusting pseudo- 

 morphs upon opaquo rhombohedra of calcite, but is also itself 

 enclosed in transparent complex scalenohedral forms of the same 

 mineral, but of later formation. Similar encrusting pseudomorphs of 

 quartz are also common, the original mineral having at timos been 

 removed, leaving an empty six-sided tube. The best examples of 

 this class are to be found at the Huron and Bohemian mines. 

 Silver occurs, both in massive lumps included in the copper and in 

 crystallized arborescent forms. The two metals have probably been 

 deposited simultaneously. 



9. Origin of the Copper. — The occurrence of native copper in the 

 cavities of amygdaloid traps has been observed under circumstances si- 

 milar to those seen on Lake Superior, in the agate-bearing melaphyre 

 of Oberstein in Ehenish Prussia, in Nova Scotia, and in the Faroe 

 Islands. Thin sheets encrusting the walls of cracks in similar rocks 



