430 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
much prehnite; that such amygdaloid belts will dip towards the lake at a 
very flat angle; and that cupriferous conglomerates are not to be looked 
for. 
Isle Royale is the only remaining portion of the copper-bearing rocks 
within the territory of the United States. It has long been known to be 
cupriferous ; the copper occurring here in the three forms of transverse 
veins, epidote courses and amygdaloid belts. Thus far mining has never 
prospered on the island. It can, however, hardly be said that the ground 
has as yet been sufficiently tested. 
