194 Rk. Pumpelly—Paragenesis of Copper 
through the presence of small flakes of rubellan; or mixed green q 
and brown, from the oxide of iron produced in the decomposi- 
tion of some of the constituents. As a rule, the greater the 
amount of rubellan the less there seems to be of magnetite 
In some instances, especially in some of the beds east of the 
Isle Royale copper-bearing bed, the rock is fine grained and sub- 
erystralline, brilliant black-green, sometimes purplish; slightl 
shimmering; easily scratched with the knife; contains consid- 
erable magnetite, small pieces of rock adhering to the magnet. 
lt weathers rusty gray. 
3. Melaphyr-porphyry ; dark-green, often nearly black; com- 
pact with perfect conchoidal fracture; very hard; contaims 
minute crystals of triclinic feldspar. 
Amygdaloids. 
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Amygdaloidal Melaphyr. ao 
All the varieties of melaphyr on Portage Lake are subjett 
to this modification, but there is a considerable variation among 
different beds in regard to the nature of the minerals im the 
amygdaloidal cavities. In all the varieties, amygdules of deless. 
ite, or calcite or quartz coated with delessite, or again spots © 
epidote, occur here and there in the body of the rock. In — , 
beds the rock is characterized throughout by the presence ® 
laumonite in small amygdules and minute seams. _ aoe 
In the belt occupying 1,000 feet or more on either side 
the Isle Royale copper-bearing bed, many of the beds aus 
towards the top amygdules of delessite and of a green flinty 
are gradually succeeded nearer the top by ovoidal, lenticular s 
eet ame 
